While I am a subcontractor currently, I think it is best to try to outsource a few tasks when you are not slammed. The VA I am working with had another contractor that she brought on before I could give her more time. Because she was not familiar with her work style she had an issue when things were hectic about a month ago with the way this person worked and handled things. Waiting gives the VA and the subcontractor a chance to get to know each other's work ethic while establishing that working relationship.
Granted the VA I work with and I had a working relationship from the corporate world, I still have to work with her to hand off things.

(I was HER team lead a few years ago!)