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? Edit: I think that my question is being misinterpreted. I know that vim is, for the most part, significantly more powerful and feature-complete then vi is. What I want to know is if there are any possible cases where vi has an advantage over vim, such as less memory use, prevalence on *nix systems, etc.