[ghaff]

Storage units are fine if:

1. It's auxiliary storage for e.g. outdoor gear you use that you can't fit in your apartment

2. It's essentially bridge storage for stuff that will be moved somewhere new (e.g. a second apartment/home) on a fairly fixed timeframe

On the other hand, it just going to be a headache for you or someone else if it's just stuff you don't have room for and don't have any real plans to have room for it. Both my brother and a friend have gone through this recently with relatives where cleaning out storage lockers was a huge PITA.