Debian user here, who has apparently missed the memo: What do snaps do that apt doesn't?
The benefits are supposed to be that they're more secure, more portable, and don't junk up your system with files strewn everywhere.
Personally I'm waiting for a better solution than anything we've seen so far for the first of those benefits, and would prefer a cross-platform user-oriented package manager like Homebrew or Nix (but better-supported-on-Linux in the former case and with a UX less like studying for a math exam in the latter) for the other two. IMO every solution to these problems on Linux desktop currently sucks to one degree or another.