I have a 60m2 shed full of stuff i've collected over the years. I'm slowly trying to go through it all and throw stuff out.
The two main problems;
1) I have, and have had, too many hobbies. These include, in no particular order, electronics, woodwork, metalwork, fish keeping, fishing, cars and probably more i cant think of right now.
2) I work in a job where a lot of "too good to throw away" stuff follows me home.
I tend to put stuff in boxes and think i'll sort it out later, but i don't.
The more space you have, the more crap you will accumulate.