use nocompilejsp option with adpatch

I have 2 question about nocomiplejsp option with adpatch.

1) usually  we use adpatch options=nocompilejsp,nocompiledb while perform patching activity. when we use nocompilejsp it will not compile jsp file during patch, so it will compile jsp files?

2) Compilejsp means what will it do exactly? As I googled I come to know it will update the outdated jsp file which are in patch. If you anything more about it, please share you knowledge.

Thanks