why do computer rentals exist?

in what circumstance would renting a computer ever be appropriate? i've always wondered. it seems to me that buying a computer would be cheaper in the long run. can anyone enlighten me..?

I know a few business do not so much rentals but rather lease them.

If you consider rental and lease the same then it does infact make a lot of sense - consider the lease agreements that I've seen usually include a clause that guarentees the latest equipment every two years or so + onsite support contract + disposal. Most if not all Universities in Canada use lease+support contracts these days.

You have to go to a show in your university, and you don't have laptop. You rent one, for one day. Problem solved. Also: change your university. It sucks for not having laptops.