Lanefan said:Where I'd rather have the powers available for other uses than the broken combo, and just restrict or ban what's broken.
Since those combos often involve very specific abilities, you would either have to make a Core Book 4: The Restrictions' Manual (page 257: "You may not get the power attack feat if you learn the spell fist of fury or vice versa"), or you'd have to ban whole ranges of character choices because of one combo ("wizards may not multiclass as fighters and vice versa" sidebar: "that's because what you can do with power attack and fist of fury")
Neither is very desirable. So it's better to design the abilities in question so that the combo doesn't work (power attack would not work with fist of fury styles, or fist of fury would not have that specific application that would make it broken with power attack) and don't create a game made up of restrictions instead of rules.
Part of the fun is finding the broken combo, even if the DM rules against it later.
What broken combo? If you take the big restrictions brush and aply it generously, the broken combos won't be there (along with a lot of things that are perfectly right).