Depends on the driver model. If you're using ASIO then it doesn't matter what you set n-Track too because it'll just use ASIO buffers.
If you're using WDM, then you should be setting your delta buffers low and your n-Track buffers high (especially if you've been following the threads related to the flaw in the delta WDM drivers).
These buffer settings determine your latency, which is the amount of time it takes from a fader move, for instance, until you hear the results of that fader move. Anything around 50-60ms seems to be acceptable for a large number of tracks, and you won't feel it. Trust me, if you've got high latency problems, you'll notice immediately because mixing will be a pain in the ass.
Latency also plays an important role in live input processing, as it determines the amount of delay you hear while monitoring your input as you're processing it. If you don't use live input processing, it doesn't matter.
Personally when I'm not using ASIO, I like to dial in my n-Track buffer settings to taste, as the preset settings are too extreme IMO. (although I always use the default high recording presets...high recording latency is fine by me, as I'd rather not risk dropouts)
Slackmaster 2000
