I sometimes suffer from mild aches and pains in my knees and hips, so after walking around all day I usually spend at least part of the evening lying on the sofa.
We adopted a small cat a couple of months ago and she likes to sleep on me in the evenings. The warmth helps with the pain, so we're both happy.
I've noticed that she tends to sleep nearest whichever joint currently hurts. So today my left knee was hurting, and this evening she has curled up on my left knee and thigh.
I have a targeted pain relief cat!