Currently llSetPrimitiveParams is the only way to both move and rotate a prim at the same time. Using an llSetRot then llSetPos has a nasty delay and looks terrible.
For child prims, the current implementation of llSetPrimitiveParams works like llSetRot, when I would think working like llSetLocalRot would be more logical. There is a way around it, by dividing the rot one is about to apply by llGetRootRotation(), but this is hacky and inefficient, and there are ugly timing issues if the root prim is rotating simultaneously.
So a version of llSetPrimitiveParams which works like llSetLocalRot would be very useful.