Sarisio: Undoable build decisions are fine if they are implemented like in Might and Magic VI, which has respawns and no level cap.
RyaReisender: Different from game to game, I'd say.
I usually have a hard time to decide for builds, up to the point where I just can't decide and just quit. More often than not I decide to distribute all points evenly on all attributes and skills because I can't decide whether I want to be a fighter or a mage. While some games can handle this well, others will just be "You can't win the game anymore". Even if it allows grinding it's often not an option unless you really grind for hours.
I like the way Avadon 1 and 2 handle it. There is a "retrain" cheat, which can be entered any time and allows you to reallocate your stats and skills at any time. (If you really want to, you can even do this during battle, but that seems a little silly.) Furthermore, later on there is a person who can give you the same effect without having to use a cheat (and with no other cost).
The Etrian Odyssey series had another interesting approach. You can deallocate skill points, but it will cost you some levels. Those games also allowed mid-game character creation exactly like Elminage Gothic, so you can try out a new build without having to delete or rest an existing character.
In Icewind Dale 1 and 2, and I believe Temple of Elemental Evil, you could permanently replace a character with a new one and use a cheat to give her the appropriate amount of experience. (Note that for IWD: Enhanced Edition you will need to load your save in multiplayer to do this.)