Mostly OT - Pressure Cooker "Seat-of-the-Pants" guidance?

Botch

Last night I kinda got lost "deep-cleaning" my convertible and by the time I came in, didn't have the energy to make up a green chile stew to cook overnight in my slow cooker.  I figured I'd get up early this morning to make it, and set the slow cooker on high; didn't happen.  At 10:30 I pulled out my pressure cooker and was eating before noon.
 
I bought my Fagor pressure cooker about 3 years ago (Cooks Illustrated "Top Rated") and also ATK's "Pressure Cooker Perfection" cookbook.  Every recipe has been a winner.  There are two variables in pressure cooker cooking: the "amount" of pressure (usually Low and High) and "pressure release", either Slow (just kill the heat and let set until it cools down enough that the pressure is gone) or Fast (run cold water over the whole cooker in the sink, OR twist the dial thingie to release the pressure directly).  Each recipe in the book specifies both.
 
The problem is, the book doesn't explain the benefits/shortcomings of each, and when I cook something I made up (often) I don't know which to do.  Today's Green Chile Stew, case in point.  The onions were softened and the pork browned just until it lost the pink, the fire-roasted tomatoes were chopped and out of a can, potatoes raw.  All dumped in the PC, set to High Pressure, and as overcooking this stew doesn't matter too much I cooked for 45 minutes (most similar recipes in the book would've gone 25 minutes).  I went with Fast Release, because I was hungry!  
 
The spuds were cooked perfectly.  The onions were completely dissolved, and the green chile nearly so.  The canned tomatoes, were still pretty much solid!  Not at all how the stew would've come out in the slow cooker.
 
So, does anyone here use a pressure cooker, and have some guidance?  I'm assuming "High" pressure cooks everything quicker, but what else?  And what do the two different pressure release methods do, how do they differ?  Thanks in advance!  

SGH

@Botch
Brother I could write volumes on this. However I am going to just hit the highlights and keep it very short and sweet. 
First, when to use low pressure? Use low pressure for “delicate” foods that are easily destroyed such as fish, crab, eggs, etc etc. You can certainly get by with using high pressure for delicate foods, but using low pressure makes the task at hand much simpler and usually produces more desirable and consistent results. 
When to use high pressure? Use high pressure 99% of the time. Again use low pressure for delicate items and high pressure for everything else. Simple enough my friend. 
Instant/Quick release. Use this release method when you are shooting for a near exact cooking time. The point of the quick release is stop the cooking process rapidly so as not to over cook whatever may be in the pot. 
Natural release. This one will seem a little more confusing but with practice it will become routine to you. The upshot of natural release is you do not have to be present if you are using a programmable pressure cooker. You can set the PC to come on and off at a predetermined time and it will naturally release on its own. This makes it sort of like using a crockpot. You just set it and forget it. With that said, this is not the case if you are using a traditional pressure cooker. You have to be there to kill the heat in that case. 
Farther more natural release is good when cooking things that have a pretty big window before being over cooked. Examples -stews, soup etc etc. 
Another way that natural release is used is carry over cooking. Once the heat is turned off the PC will remain under pressure for considerable time and as such will continue to cook. The times vary greatly between different PC’s but it’s in the 15-35 minute range depending on the model. 
This last one you will figure out as you use your PC more and more. There are some foods/dishes that just turn out better if you use a instant/quick release and there are some that turn out better if you use a natural release. It would take me forever to try and type which ones work best with what. However as luck would have it, if you Google “PC recipes” they almost always give the preferred method for the food that you are preparing. It has been my experience that their recommendation is usually correct. 
I hope that this helps a little my friend. 

HeavyG

I seem to recall that one of the potential problems with some recipes is that if you use the fast release is that the sudden loss of pressure can create "foaming" which could expand and clog the release valve.

If one pays close attention to the max fill level (which varies depending on the type of food being cooked) that may be less of a problem during a fast release.

Carolina Q

I always thought that one of the Quick Release vs Natural Release differences involved cook time. The Nat Rls method means that the food cooks longer. If the recipe calls for Natural and you Quick Rls it, that particular dish may not be done. And if you do a nat rls when the recipe calls for quick, the food will cook longer and may overcook. Plus there's the foaming issue for certain foods as already mentioned (dried beans in particular I understand are susceptible to this). 

I usually follow recipes specifically for PCs and just do whichever it says.

caliking

Pressure cookers have been standard issue in just about every Indian household for decades. And its always been "seat of the pants" as far as recipes go, because most families pass down recipes with instructions like " cook for 'x' whistles" since most pressure cookers in India are made with this bob valve/weight thingy that releases pressure intermittently. 

Given that context/background, quick release is for foods that won't benefit from prolonged pressure after the heat is turned off. For example, when we're cooking lentils, if we want some texture then we quick release. If we dont care about that, and are okay with a more soupy or homogenous texture, then we go for "natural pressure release" or whatever its called.

As far as most Indian cooking goes, it doesn't make that much of a difference (depending on how anal you are about certain textures of foods". In my case, it depends more on how impatient I am. If I have time, I'll turn off the heat earlier and let the pressure release on its own as I do other things. If not, lift the bob, release pressure, and get on with it. 

Botch

Thanks for your comments, folks, they make sense and I think I have a better feel for things.
For the record, after eating my first bowl I decided to dice up and add one more potato, and then simmer the soup for 60 more minutes, sans pressure.  The new potato was cooked perfect, the old potato broke down a bit, thickening the stew, and the tomatoes finally dissolved.  Different textures, but both tasted great!  
 
EDIT:  Never would've thought to cook fish or crab in the PC; added to the List.  

SGH

@Botch
If you ever get real deep into pressure cooking and/or canning, give All American a look. There products are second none. With that said, the average person need not spend the money.