Well you CAN advance the timing a bit with altitude, but this practice actually comes from automotive circles. Back when you could set your own timing, it was common practice to add 1 degree of advance per 1000' of altitude above Sea Level, to the manufacturer's specs as it provided better performance and by that I mean better acceleration.

Cranking the timing too far forward and it'll make the engine hard to start as it fires way too early in relation to where the piston is at in it's stroke to the top. Ask any of the old Chevy guys what happens when the timing is too hot????

Then there is the issue with what we used to call "pinging" if the timing was too far advanced and that is actually detonation which is really hard on an engine.

For our purposes, there's not really much of an advantage where we run most of the time at a more or less constant RPM with gradual power changes. To some extent whether or not it might help kind of depends on the ignition. Is it a mag setup? an electronic? what does the advance curve look like? and so on.

In my own experimenting here a 4500'ASL, I don't find there is any advantage to ground RPM readings on my stuff with electronic ignition modules but there does seem to be a bit more heat generated if I check those temps on landing each time I play with the timing. Now these are just anecdotal observations with no specific attempt to show a direct correlation so whether or not it's actually true I can't say. I can say that I don't see any performance increase by advancing the timing, so I leave mine where the manufacturer specs them.

JMHO, YMMV....[8D]

Oh, for what it's worth you don't set the timing up for full scale stuff. If a Continental or Lycoming manual calls for 24 degrees of advance, that's where you set 'em and that's for magneto equiped engines which have either a separate point set or impulse couplings on the mags to retard the timing for starting.