Multiplexing in the ssh shell is way more convenient than opening a new ssh connection every time you need a new terminal. If vim is occupying your shell you definitely want a multiplexer instead of Ctrl+Z every time you need to do something in shell. I know vim 8 has an integrated terminal but I can't stand using the terminal with vim keystrokes.

tmux is also amazing for spotty ssh connections. For example, I had to run long jobs over ssh through a VPN. Tmux means you don't need to worry about the connection dropping and losing your current process