Can't speak for anyone but myself, but as a Junior, I have to concur.
I recently joined a new job and got sent to a client, primarily for ticketting, until I was given a project to work on from scratch. I have to say, the codebase was quite big and most of all needlessly complex, and I had to take three days just to get a quick grasp at the code section on which I had to work (a single Symfony bundle with dependencies). The ticket itself took me barely half a day to resolve.
So basically I'd say it depends on factors such as the project, complexity of codebase, the amount of time you can spare to show him/her the code and answer his/her questions, and such. It also depends on the estimated time you will gain once this new person will be effective. So if you truly are in a hurry, and a big one, I'd say it's not worth it.