If you use the right fuel then detonation isn't an issue.

Want to trade your hectik sticker for some fully sik ones? I don't have a hectik one yet ;)

The vacuum advance thingie is there to compensate for the lack of mechanical advance at lower rpm's where there is a mostly closed throttle plate, if you mash on the gas, even at low rpm, you'll loose much of the vacuum advance too. like how the brakes don't work well if you're at WOT and trying to modulate the brakes.