To expand Wootah's comment; stack splitting helps with shops too. If you're a few zorkmids short of an item, selling 7 of your 8 Smithing Kits is nice; selling all 8 could mean you won't find a kit for the next 5 floors :/ If there was no stack splitting you'd have to head to the Pocket Dimension every time you found one and put it in it's own floor space, and that takes a little bit longer than pressing Alt. Same for transmutes. Having to drop every gem you have, then picking up the new one, then transmuting it, then finding a spot on the floor for it...yuck. I split for those things far more often than I split for Lutefisk; Lutefisk is typically "oh I found a shrine on floor 9+, I have 350 softballs and 422 bolts, might as well Skol some of the ones I don't need and add them to the pile of ~150 lutefisk that I've been turning Rusty Caltrops/Apples/Sewer Brews/etc into."