Ant T,
you are correct, there is nothing in limitations that requires you to disengage the AFCS after landing.
However, from experience I can tell you that the a/c is far more stable on the ground with it off. I'm sure you have seen many pilots have the old girl do a "dance" immediately after touch down, this is the interaction of the AFCS. The next time you land, as soon as you have all 3 wheels on the ground (and there is no chance of lifting off) release the AFCS. You will see the a/c go stable.
When you are testing the AFCS on the ground and you have the monitor switch in Roll does the needle follow the stick or go opposite? Now when you are in flight and do the same thing what does the needle do? Why?
Also, taxiing with it on has a noticeable effect. I know, the micro switches should make it not matter, but just try it. Ground taxi with turns with it on and with it off and tell me which "feels" better.
The OP was asking for opinions and those are mine, not trying to tell anyone they are doing anything wrong or to change their ways.