Many MMORPGs torture their players with ridiculously tight storage limits. There may conceivably once have been some kind of server side resource limitations which required these limits but I personally think it is a stupid game mechanic which upsets every player at some point in the game.
Thankfully EVE has not gone down this route. Individual ships have limited cargo carrying capacity but you can store as much stuff as you want in a space station.In fact you can have separate unlimited stores in every one of the thousands of space stations in the game.
Such bountiful storage is a godsend for those of an acquisitive nature but it does bring its own housekeeping problems. I must put my own guilty hand up and admit that after less than three months in game I have a tally of 492 items in storage spread across 13 solar systems. That doesn't even count the stuff stashed in the holds and fittings of any of my 12 spaceships.
Some of this clutter is the result of foolish buy orders placed in the early days when I imagined I could make a living as a trader. At the time it seemed like a good idea to place region wide buy orders for stuff at low prices. I overlooked the fact that I would have to actually fly to all these out of the way places to collect the stuff in order to sell it again at a profit. Somehow I never quite got around to making all the 20 hop round trips through low security space to collect those 10 piece lots of small projectile ammunition.
It is not just that however because in addition to allowing unlimited storage capability Eve has a number of features which encourage you to accumulate stuff.
First off the fact is that nearly all of the loot you pick up is actually useful. In other mmorpgs the level 1 rusty letter opener becomes completely pointless (!) once you have gotten your hands on a level 2 bread knife of uberness. In Eve even the cheapest tech 1 module can still be useful - perhaps filling out the last slot in a build or maybe helping you to experiment with a throw away frigate.
Closely allied to the above is the fact that stuff gets destroyed so you need replacements. My battle cruiser already has its full complement of auto cannons, but If I pick up another one I'll probably hold onto it, just in case.
Eve doesn't funnel player into certain roles. Just because I am a mission runner today doesn't mean I can't try mining tomorrow or freight hauling or pvp. Even stuff that is of no interest to you now may be useful at some future date. If I pick up a Tridiagonal Dilithium Crystal Sensoriser I may have no idea what it does but I might still hang on to it just in case it turns out to be useful later.
Also you can keep as many ships as you like and each ship needs its own complement of modules. You may want to experiment with different fittings, different builds and different tactics for any given ship. All good reasons for holding on to stuff rather than selling it.
Even if you finally decide that you really don't need to hang on to 42 small Microwarp Drives there may still be reasons not to sell straight away. The dynamic nature of EVE's economy often means that you will get a better price by holding onto it for you next trip to Rens or Hek or Jita or where ever.
Anyway they are all my excuses for keeping so much junk. I have to admit they don't seem quite so convincing when I have to wade through 200 items in my inventory to find that medium armour repairer I need for my current ship. Perhaps I ought to follow Winterblink's lead and do a clean out.