That is only useful in Windows XP. And even if you use XP you should experiment with different settings when your CPU consumption is high, at 80%^. For Windows 7 ^ leave it on default or try to experiment with it in the same manner. Sometimes, with some audio cards, it has to be set differently and there's no easy rule for that. Like, RME drivers work best with the default settings for me, even on XP.

 

It doesn't work always. It's a tip for minimum ASIO latency, a situation not given in other kind of optimizations (games, video, etc) . But depending on your audio software and hardware it may be even negative as you say. I don't even use it because for me latency is not an issue (I don't play live).

Depends of your needs and the software you've installed. In my desktop computer I've all wifi services disabled because I'm in ethernet wire, in my laptop I can't. If you can afford no internet (tipically in a dedicated PC or Windows partition) disable all network services. Disk indexer is one of the hungrier services. I've a batch command file to disable it when I look for maximum performance.

And then there's services installed by third party software: antimalware, disk backup (acronis), updaters of all kind (browser, flash player, etc..). In fact Windows Update it's really resource intensive, but if you have a fast computer setting it to notifications only does the trick.