Apps that won't let phone sleep??

[QuasarZ]

When I go to install an app it pulls up a new screen that says something like this program has access to the following system tools "won't allow phone to sleep"

What is the deal with that? If you install an app or game that says this, will the phone always be in an awake state and drain the battery constantly? Also why do so many apps have access to so much of your "system tools"?

Thanks a lot.