Interning "for a few weeks" means that you miss out on candidates who already have perfectly good jobs. These are often the folks that you are trying to hire.

Interning "for a few weeks" means that you miss out on candidates who already have perfectly good jobs. These are often the folks that you are trying to hire. So imagine how a candidate reacts to, "Well, while we know you're happy where you are, what would you think about quitting your current job so you can try out a position at our company for a few weeks?" (Note that candidates can't use vacation time just to do a try-out, for legal reasons, and may be reluctant to use up all their vacation time in any event). Having a trial period puts all the risk on the candidate, and guarantees you're filtering out people that you'd otherwise want.