Parts lockers - Am I missing something?

[PREdaTOR]

So I have built 2 parts lockers and I have to admit they do not work the way I expected.
When I built my first one I thought it would allow multiple versions of the same 'part' to be stored, like doors or wheels but now, you can only fit one item in each slot.
The weird part is the room in each spot is way too big for just one part so am I missing something?
Also, why would you have more than one pneumatic locker since they appear to be endless storage? (I have two, but only to store all the excess paints etc)!

[Mack87]

Just a note but I kept the original engine just in case and I store it in the parts locker. The engine is really big so I think that's why the parts locker is so big. Especially when you build the later engines one may be good for a mission with lots of gas but another may be good when you can generate a lot of energy. Just a thought, not an authority.

[HalleysComet]

You can see parts name directly within locker, it is designed to let you find and switch parts quicker (imagine try to find a specific part within a lot of material, it would be a pain in the ass)

[Lord Caveman]

There are twelve spaces in a parts locker, which nicely fits the amount of parts you could expect to change out frequently: five doors, five panels and two bumpers. I have a locker for each resistance type and as I'm typing this out I wonder what the ratio of driving/garage noodling is in my 45h playthrough.

[PREdaTOR]

Thanks all, a couple of things I hadn't considered: Engine size as I haven't replaced the engine yet (though I have unlocked all but the last one), and full parts swap outs.