It’s, as you said, because it mounts everything as root. It’s possible that this could be exploited to gain root privileges but not likely. If you’re paranoid and/or building a secure system that you don’t need to dual boot, it’s not a bad idea to disable it.
Literally everything. iMessage is a real messaging app with all of the bells and whistles. Blue means all of the features you want will work. Green means SMS, which is garbage.
iMessage gets you end to end encryption, read receipts, reactions, larger media sharing, functal group chats, and more.
RCS solves some of the shortcomings of SMS but it’s not a feature that Apple supports.
What do you mean exactly? Nearly every house in Colorado has a basement.