generally on a pump gas car, 9 times out of 10 your going to be octane limited so the advice of "running as much as you can" is what you will do. but times where your running a higher octane fuel or alchohol or meth injection (something that has/increases octane) the idea of running as much as you can doesnt work any more.
remember the goal with timing is to get peak cylinder pressure a few degrees ATDC, and since it takes time for the flame to expand from the moment of ignition to the cylinder walls, timing advance must be increased, at higher engine speeds it needs advances even further, to compensate for the fact that the flame speed remains relatively the same but since the engine speed is faster, you need to fire the spark sooner to keep the peak pressure in the cylinder at the same point (few degress ATDC)
so for each given engine state, wheter it be idle, part throttle, WOT in the mid range or at higher RPM, each give state will have its own "sweet spot"
this is where octane comes into play, if you have enough octane to reach that sweet spot or MBT (maximum brake torque) then you run that, advance it any more and your peak pressure doesnt happen where it should and you start fighting more cylinder pressure as the piston approches TDC. what happens then is your cylinder pressure it used more in pushing back on the piston approaching TDC, rather than pushing the piston down ATDC like it should be doing. not to mention it also increases the chances of knock.
if you dont run enough, you peak pressure happens too late and you piston runs from your flame in a sense and you lose pressure either scenario decreases torque/power.
these two scenarios are describing more of the extreme ends of too much advance or retard, but you get the idea of whats starts happening as you eith run too much or not enough. you have to remember this all happens within milliseconds and every little detail makes a difference.
like i said before on most street cars or w/e running pump gas, the octane simply isnt enough to get to that sweet spot at WOT with knock, so you just "run as much as you can" and thats as close as you get. until you get a higher octane fuel or something.
another thing to note, anything a person can do to speed up the flame speed will make more power, like combustion chamer design and etc.
what this does it let you run LESS timing, and make more power, reason is that with less timing, and a faster flame speed. its less time during the engine stroke that the piston has to fight an ever increasing pressure as it approaches TDC.
since every engine has its own attitude and is different, just advance it as much as you can with pump gas until you get knock and then back it off some. but its all more or less guess work, IMO its pretty difficult to feel a power difference when adding a few degrees timing here and there. the only real and accurate way to do it is to get on a dyno and measure power output as you change timing.
