EVERY 20 TICKS DO
  INPUT FROM mob_loot
  OUTPUT TO EMPTY SLOTS IN storage
END

Without the EMPTY SLOTS IN modifier, SFM will try and stack items.
If the destination is 1000 slots containing pickles, then inputting a sword will have to check each slot for compatibility.

Users could then make an infrequent condensing loop that does

EVERY 300 SECONDS DO
  INPUT FROM storage
  OUTPUT TO storage
END

to try and stack applicable items

https://github.com/TeamDman/SuperFactoryManager/releases/tag/4.25.0-1.21.1