Knee pains essentially. I run 150mm cranks on all my bikes because my knees are trashed. For recumbents specifically, it's quite well known that short cranks are almost always a good idea: they give better performances (you spin much more easily) and they save your knees even more than on an upright. Many riders who have no trouble on an upright but experience knee pains on a bent solve their problem with shorter cranks. Many recumbentists without problems who switch to shorter cranks go faster and climb better as well. Personally, beside saving my knees, short cranks give me 2kph on the flat, and allow me to continue spinning comfortably above 50kph going downhill with a 44/11 combo.

This time I went with the "luxury" option (i.e. homebrew 150mm cranks with a spider that can take my favorite chainring sizes) instead of a crummy child crankset with riveted steel rings. I think I'll do that with the other bikes too. Too bad it snows today, I'm dying to go ride