Compass card-why bother?

[foxmoth]

Switching on pitot heat, landing lights or any other high energy load doesn't usualy effect the compass much...couple of degrees.

This will actually depend upon the aircraft and the heading you are on - with some aircraft on certain headings this can be considerably more than "...couple of degrees"!!

[Oktas8]

Compasses are swung with the engine running and all electrics switched on!

Maybe in your part of the world...