installed a 15t sprocket or a 43t sprocket?

Yes.

Before I only had suspension and cosmetic mods.  The advancer is great for better throttle response down low.  My bike saw a huge gain because I have a CA model.  

CA model is 5 degrees initial advance
Others is 12 degrees initial I think
Bob's bumps it to 17 degrees initial

I had to adjust my idle once the bike warmed up but I never have a heat problem with the new advancer.

So do you always have to adjust your idle switch with the advancer?

only when I first installed it.  12 degrees (I have a CA bike) change in intial advance is drastic and would affect idle.  Once its set, you shouldn't have to touch it.  If your seasonal changes are big enough, you may need to adjust for that too.  I don't recall my bike needing any idle adjustment since when I first installed the advancer