Is fatigue actually detrimental?

I know in IWD fatigue lowered your attack roll by 1. You could only score 1 -19 and never get a critical hit. It doesn't seem to do anything in BG 1 or 2. You can fight with fatigue and not appear to have any deficits. And (despite Dynaheir saying 'magic does not rest well in a tired mind') there is no spellcasting failure.
Given the current engine is it possible to mod fatigue so it actually is a noticeable problem?