Since the toddler patch I've noticed two things:
1. Many times if a Sim is going off to perform an action at a particular location -- like walking to the back of the lot to mourn a dead relative, or walking to a room on the other side of the house to play a musical instrument -- and I will cancel the action and queue up something else, the original action disappears, BUT they keep walking to wherever they were originally going, then turn back and do whatever I told them to do instead.
2. When I send them to use the toilet or tub, their bladder or hygiene bar will start to refill before they ever get to the toilet or tub.