Windows 10 to my mind is much cleaner and simpler, much easier to use; in some respects it feels somewhat like a return to XP, whereas 7 was in retrospect a bit of a clunky aberration. I don't see why you'd want both 7 and 10 unless you have some specific reason to do so [in which case you'd already know].
From time to time I toy with the notion of merging my Vista/XP and 10/XP boxes together to make a Vista/10/XP/XP monster; the reason for keeping those OSs all running separately is pretty much the same reason people run VMs: to keep certain things ringfenced, to maintain old software [and two machines to give some backup ability]. Doesn't sound as though any of that is on your mind.
I think it's easy to get in the habit of keeping too many OSs running for the sake of it. I'd only do so where there is a genuine need. That said,lately I keep wondering whether I need a baremetal install of linux; think I'm just bored though 🤣 .