A junior programmer fresh out of Uni, joining my team. Learning a new language / framework / application, working full time. Will usually take more of my time to help them than if I just wrote the code myself. I have to explain which existing functions they should use. I still have to flesh out most of the design and implementation of the tasks they are assigned. I may need to take over their keyboard and type some of the code in for them, as the fastest way to get the point across that I'm trying to teach them. And getting their patches up to scratch can take a number of iterations.
After about 3 months, this equation should start to shift. Even though they will still take far longer to complete a task than I would, it should take less of my time to get the same work done. At this point, the addition of someone to the team starts to pay back the initial training period. We can evaluate if this new person is still worth investing time in.
And that's for the graduates that I'd consider hiring in the first place. Most CompSci graduates I wouldn't consider employing at all.