In my case, as merchant, when I make an outfit, normally 7 to 9 colors each, I try to be as organized as possible, that means I make 1 folder per color for the textures and in that same folder I drag all the things that I'm creating for each color (Some outfits had more than 200 textures ._.)
Due to this, my inventory was over 100K items and it always took me around 2-3 hours to finally being able to login to SL, no matter what viewer I was using. Now my inventory is 88K, still take me a few minutes to login but better to wait minutes than hours D:
Boxing items is the best option to save space for textures/objects (at least for me) and if some day I want to wear some of the things i create then I just go and open the box.
I know it can be annoying sometimes to open boxes -> wait until it loads -> delete -> clean trash etc, but you need to put yourself in some merchant's position. More inentory to load = slower SL -> Slower SL = Annoying way to work.
And as costumer, I prefer to get boxes, sometimes i buy a dress, wear it, then delete it, I want to wear it again? just go and open the box, simple as that, and is better that way than keep doing useless space and making the inventory list longer.
At least imo