We rented a small storage unit in our daughter's college town for the summer -- several summers, actually. It was cheaper than renting a van to bring her stuff home (my small car would've required multiple trips home, which would've cost both time and money). She didn't need her college bedding, towels, chair, lamps, printer, dishes, winter clothes, etc., and I didn't 'specially want it all piled up in our house. She and her roommate together filled (but didn't pack tight) the smallest unit available, which I think was 5x5.
For those few months, it was a good deal, especially when split with the roommate.
However, when we rented the unit, the guy asked if we wanted insurance. I declined, saying that the items weren't really of much value -- this was a matter of short-term convenience, given that she'd want them again in just a few months. He laughed and replied that nothing stored in his units was actually valuable.