The sleep policy controls how much sleep time the RunUserInterface message loop takes. Settings the to "Do not sleep" will result in CVI processing messages as fast as possible, but this results in the CVI app taking up more CPU time. So if you want to ensure that your CVI app processes all the messages ASAP, you could change this setting and this would make your app "feel" faster but your CPU usage will go up.
In most cases, you should not need to change this setting to get more responsiveness from an application. Designing an application to run in a concurrent fashion (multiple threads for multiple tasks) should be the way to go. But it's hard for me to pinpoint how many threads becuase this is very application and machine dependant, especially with dual core systems and hyperthreading now becoming avalable to the masses. It is best to experiment with your application and see what works best with you.
Here is another document that talks about optimizing your CVI application. I hope this helps.
Bilal Durrani
NI