What will enabling flying do?

[iron_leonem]

One of the residents of my server is begging me to set the server properties for flying enabled to be true. He won't tell me what it's for, and I want to make sure I know what I'm getting myself in to. What possible abuses and cheats, or misuses of items are possible with flying enabled? Thanks!

[Kalbintion]

With flying enabled you can exploit glitches, use hacked/modified clients, etc to bypass flying restrictions when it shouldnt be possible. If the person is asking but not providing a reason why, I wouldn't do it.