Back in the "old days" when this stuff called petrol was available things were a little different .
You retarded the spark, started the bike, allowed it to warm set it to full advance and forget about timing unless you are on a long slow hill.
However now days with this stuff called "fuel" which is nothing like petrol, unless you are happy to wear out your left thumb or run plugs 4 grades hotter than standard it is a more of a wank item than a benefit to the running of the bike.
I really notice it when riding in groups and we come to either some steep downhill twisties or long sweepers.
The std bikes with aa units wizz strait through, the manual bikes generally either pink, backfire or even load up a plug and loose a cylinder till it clears up a bit further down the road if at all.
Only one rider with a manual ignition seems to have it down pat, but he has ridden the same bike for 55 years having ridden it from new in 1950 so he knows exactly when and by exactly how much to drop the ignition back and when to forget the ignition and go back a gear.
Sitting around Ken it was very interesting watching the left thumb , he was forever tweaking the timing but by now I imagine he does it involuntarily.
Over the thousands of miles I have ridden with the group, Ken is the only riders with manual timing that has not needed to change a plug at some point in time and his bike always runs well. Mind you going up a hill behind him with his throttle wide open and the timing back a few degrees was music to the ears and a treasured BSA memory.