May only be minor, but when you put the caliper back on it may not be in 'exactly' the same place, which may cause a tiny bit of friction.
I cleaned my rear caliper a few weeks ago and i think i must've swapped the pads over each side, that caused friction for a while as well but it didn't last long, they just need reseating for a while.
Also, if the wheel is, for instance, aligned 1mm different left or right to how it was before the pads will need to adjust again on the discs to compensate.