dtgreene: ...allows you to basically skip Chapter 2. (It's not the only skip in BG2; Chapter 4 can be skipped with another trick (polymorph teleporting), and Chapter 5 can be basically skipped by attacking the dragon who's supposed to help you
Hickory: Just throw the game away. Much easier.
I wouldn't pooh-pooh things this dismissively, although it's mostly not all that useful except for speed run challenges (where you more or less MUST use glitches before long to be relevant, as you can not generally beat record times without using at least the same level of engine exploit as the existing holder did. Makes me quite sad in Doom in particular as there are many levels that I will never again get to see a "normal" frantic speedrun because some little mapping oversight allows an exploit to skip much of the map that a normal or 100%-run player wouldn't use but a speedrun player must to be competitive).
Going one by one -
* Bypassing Chapter 2 doesn't really gain you anything except saving the time to gather up the gold (only relevant in a speed run); Chapter 2 and 3 are essentially identical in what is accessible apart from needing to trigger Chapter 3 and its associated main quests in order to proceed to Chapter 4. (Indeed, especially depending on which side you pick, Chapter 3 just makes sidequesting harder without really benefiting you in any useful way compared to staying in Chapter 2)
* Bypassing Chapter 4 is only useful in a speed run. Otherwise it actually impairs you as you miss out on a lot of useful stuff (as you can not return to the Chapter 4 areas once having left them).
* Killing the dragon in Chapter 5 is actually useful to Evil parties, however; her blood is a component for the Human Flesh Armour which is actually a very nice one for evil characters. (It can also be useful to Good parties who are in a pickle due to being inadequately leveled/prepared for the Underdark, because then you have only one challenging opponent to blast through, compared to the multiple difficult zones of doing the main quest "normally")
Sarisio: Thanks for that list, do you have similar list for IWD2? That one game I never finished, so I will most likely replay it first.
IWD2 also has comparatively few points of no return that I can recall:
* Once you leave Targos on the Airship you cannot return.
* Once you leave Z'hinda Citadel (I'll just say it's a big round single-level maze, you'll recognise it immediately by that description) via the North-East exit, you can no longer return to previous areas. (The door locks behind you and cannot be opened by spells or a Rogue, so you must proceed to Chapter 5 which officially sawtooths you off from earlier areas). There is one exception, but when you do return to that area, it's going to be a different area ID than when you previously visited, so you won't be able to retrieve anything that you left there then.
I've pretty much only just gotten to Chapter 5, and haven't finished the game, so I'm fuzzy but I'm pretty sure these are all the remaining ones:
* Once you kill the boss enemy in Chult Jungle you must run for it to leave the area (or game over), and you won't be able to return.
* Once you finish the quest in Dragon's Eye level 4 I'm *pretty* sure you won't be able to return there (I may be wrong)
* Once you activate the final encounter in Severed Hand, you are automatically forced there when you leave the area that you activate it in, and therefore this prevents you from returning to any other previous area at all.