Continued use of the same dripping for frying - is it advisable? I fry lamb chops and leave the dripping in the pan where it solidifies. Next time I cook something, the lamb dripping imparts extra flavour.
I have heard that some people just wipe a frying pan instead of washing the grease off. I don't even wipe the pan - I let it build up.
My reasoning is that (a) dripping doesn't go off and (b) any germs/bacteria would be killed by the heat of frying.
Note: I leave the pan covered by a lid when not in use.
Is there any reason that I shouldn't continue with this practice?
Firstly, I would challenge both of your assumptions.

(a) dripping doesn't go off

Like any other fat, lamb drippings can and will go rancid over time.

(b) any germs/bacteria would be killed by the heat of frying

While it's true that any molds or bacteria themselves will be killed by heat, the same does not hold for any toxins they may have produced.
Secondly, when you fry anything, you introduce small particles into the cooking fat. These will burn and -- health risks aside as they are off-topic for this site -- start ruining the flavour of the fat.
You can cook using animal fat rendered from lamb chops, or pork chops, or bacon, etcetera, but you should filter the fat, keep it refrigerated and cannot expect to reuse it indefinitely.