When off is a preposition, the phrase off of could almost always be shortened to just off. The unnecessary of is common in informal speech and writing, though, and using it is never a serious usage error. But writers who value concision can avoid it.
For example, of could be removed from each of these sentences:
It could wean the US off of foreign oil. [State Impact]
Sarah Palin was nearly pulled off of Fox News because she announced that she was not running for president on a rival broadcaster. [Daily Mail]
In the end, the NBA, coming off of a highly lucrative and exciting season, should not suffer too much. [Toronto Sun]
He claims it has profited off of its “false affiliation” with him. [Stuff.co.nz]