The differences that actually matter are self explanatory: map is for all modes, imap for insert mode, nmap for normal mode and vmap for visual mode (& tmap for terminal mode in NeoVim). The rest can be safely ignored as far as I can tell.

Little confession: I have no idea what e.g. the difference between "nmap" and "nnoremap" is. But after years of randomly mixing them in hundreds of bindings without a noticeable difference it doesn't seem to matter. Just use map, nmap, imap and vmap, avoid duplicates and everything will be fine imho.

You're right, for most simple use cases it doesn't matter. But I once spent an hour on a weird bug that turned out to just be some plugin applying a map that I didn't know about and that I didn't know about map expansion. So I might be biased, but I think a loose understanding is helpful.

The default behavior is to recursively expand and apply your mappings and "noremap" disables this recursion. For example if you do something like

  :map j k
  :map q j
  :noremap w j

q is expanded to k, but w is expanded to j

Thanks for this example, now I get it. It never really clicked for me when I read explanations on SO etc.

nnoremap is "non-recursive remap" since I think its possible to chain nmaps (`nmap A B, nmap B C` will map A to C)

I find that I never want "map" functionality, so I do the opposite, always use "noremap".