Igntition timing
 

It says on the GasGas EC 125 2006 manual that ignition should be timed to 1mm BTDC. Is it really neccessary to time it? I just put the ignition plate in the middle of the adjustable space and it runs good. Ive heard that you change the temps of the exhausts etc by messing with the timings. Could someone explain further? Also, how does the heat grading on spark plugs work? When do you need a colder or hotter plug. I dont need it, im just asking for knowledge