Vi vs vim, or, is there any reason why I would ever want to use vi?

I know a bit about *NIX text editors (currently migrating from nano to vim), and, after looking around a bit on the Unix & Linux SE, have noticed that vi is used instead of ‘vim’ in a fair number of questions. I know that ‘vim’ stands for ‘Vi IMproved’, and, with that in mind, am wondering why anyone would rather use vi instead of vim. Does vi have any significant advantage over vim?