Theoretically, the smart setting does not affect performance. I turn
mine off for recording, but turn it on occasionally to check the
condition of the hard drive. Get Active Smart software and you can see
a lot of stuff going on in the drive, of which temperature and error
rate are the key ingredients.

If you have a seagate drive, it may surprise you to know that the
default setting is set a bit slow--the SMART won't help with this but
there is software that allows you to turn up the speed--good for
audio.

A seagate drive and a 92mm super quiet fan turn a fostex hard disk
recorder into a stealth recorder (esp d824, d1624 and other models on
this frame)
jj