I use Pow-r 3 for final mixdowns. I have 'None' selected for this particular setting, but I don't generally have any conversions going on until the final. At that point I select my dither option in the bounce dialog. Yes, I believe it matters for sound quality. Performance isn't really a problem considering when it is applied.
There is a pretty good write up on when it is applied and some considerations for which to use in the Help topic
http://www.cakewalk.com/D...age=3&help=0x22B19