use of i

Mixing them up is always a mistake, but of and off are commonly confused nonetheless. Below, we’ve listed some common situations where you want to use of and some where off is the correct choice.
We use of when we want to show that people or things relate to other things or people. For example, when we want to say that something or someone belongs to or is a part of something or someone else, we can do it like this:

What was the use of all that noise and crowding and piggish hurry?
“If there were any use in wishing, I’d wish myself on shore,” said the second.

References:

http://www.thesaurus.com/browse/use
http://study.com/academy/answer/what-is-the-plural-of-thesis.html