My final calculus was adding up what I had spent on storage units, and realizing it was way more than the replacement cost of most of the crap, so I reduced it down to personal momentos only.
In general, based on various family/partner-related experiences, is that you either have a specific I need more room for a specific set of activities that I have a concrete plan to use OR I have a specific plan to have more space for this crap--which I want to keep. A lot of people pay for storage space with no real plan which is just going to be tossed at some point anyway.
A while ago I read something along the lines of, clutter is a delayed decision. That's what most storage units are. People don't want to make a decision today, so they stick it in a storage unit and pay on it monthly so they can make the decision later... or the decision gets made for them.
I think that's about right and it's even OK to a point. Sometimes I do come back to hobbies, etc. Or it takes that 5 years to be confident I'm really not going to wear this clothing again. But keeping stuff "just in case" is definitely a tendency to keep under control or it gets to a point where dealing with clutter is such a chore that many people lie down until the impulse to deal with it goes away.