lately i encountered a little nuisance with the ik handle tool (rps) which confused me as a beginner in rigging. i’ll illustrate the situation as follows:
go to top view and draw three joints with grid snap (x) on. the three joints should be perfectly aligned this way now: as you know, this makes the ik solver go crazy so you normally position the joints with a little bend so the ik solves correctly out of the box. you may think that you can just move the middle joint a bit up or down to have a slight angle, but if you try to add the ik solution, the three joints will straighten out, which surprised me.
the reason is that maya stores an initial preferred angle value when creating the joints. so basically the ik solution will straighten out the three joints again, even when i moved the middle joint around to create a slight angle. so you need to set the preferred angle again after you moved the middle joint to overwrite with a new value.
with the assume preferred angle you can check which value has been stored into your bones, so you may double check your rig when you set your preferred angle. setting a preferred angle in a rig is also very helpful to have an additional ‘backdoor’: if you select edit > select hierarchy and set preferred angle, you can save all the angles in your character’s default position. with assume preferred angle you can get the default angle back very easily. these kind of fallbacks are always welcome for animators in production phase.