FWIW, I find the default binding of C-z totally useless and a waste of
a good keybinding. I rebound it as a prefix key for my keymap
containing lots of useful commands.
Also FWIW, I also find the default not only useless, but annoying. I have rebound it to scrolling down by one line (and M-z for scrolling down). Those mappings come from the gosmacs bindings that used to be part of GNU Emacs until they were removed.
Regards,
Elias