what's the difference between kIOPMAssertionTypePreventUserIdleSystemSleep and kIOPMAssertionTypeNoIdleSleep?

I'm develop an app for prevent sleep in Mac, trying to use the api IOPMAssertionCreateWithName, but I'm confused for whether I should use kIOPMAssertionTypePreventUserIdleSystemSleep or kIOPMAssertionTypeNoIdleSleep. In other words, I want to know what's the difference between kIOPMAssertionTypePreventUserIdleSystemSleep and kIOPMAssertionTypeNoIdleSleep?