The only reason I see for having multiple systems is when you have multiple rooms.
For example, you may have a system for your "man cave" HT room, family/living room, and bedroom.
But in reality, if you didn't have a man cave and your bedroom isn't suitable for a speaker system, then there is no reason you can't just have one system to rule them all.
A great speaker system will be great for everything.
My new HT room will have a keyless door lock for sure.
House guests can enjoy my sophisticate Linkwitz Orion 2CH "Music" system.