Most cams have advance ground into them and you don't need to advance further unless that is what your engine and combination like best. There is no rule, but most cams have about 4 degrees advance already, if you install dot to dot and check to make sure it is accurate by degreeing the cam.
I think chain stretch is a misnomer as the chain doesn't exactly stretch, but rather the links wear and the timing can be affected by that.
So, in my opinion no, you don't need to advance most cams a couple of degrees for chain stretch. Just make sure it is where you want it, preferably degreed with a degree wheel.
JMO,
paulie