What's the purpose of scheduling raids?

I mean, I guess more manpower if you schedule it at a certain time since everyone can get ready but almost every single raid I participated in are fastburn ones and easily the best.
The best raids just happen whenever people least expect it, trying to schedule raids in advance is retarded.
Also expecting that your enemy isn't actively lurking here is retarded. Scheduling whenever you're going to raid something is just going to let the jannies know when you guys are active. *cough cough operation soyclipse*