Why does my computer wake up from sleep and then go back to sleep on its own while in sleep mode?

Apr 4, 2015
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I I recently built my own computer a while ago running Windows 8.1.

I put it on sleep mode and 30 minutes later I see it turns on for like 15 seconds and then it goes back to sleep without me touching it.

Is this a maintenance thing by Windows 8?
Also, it turned on by itself once and apparently that's a Windows 8 maintenance feature.
Is sleep mode also bad to use often? Like wear and tear?

Thank you, God bless!