Yes, it is important to not "lug" then engine at too low rpms, with a high load such as going up hills. The ignition system has no auto-retard mechanism, and the mechanical advance goes full advanced very early in the rpm range. It is very easy to encounter a condition where the load is too high for the ignition advance to deal with, and ping occurs, which is potentially damaging to the engine.
So, when going up hills or riding with two-up, and if you feel the engine laboring and needing large throttle openings to deal with it, then you should downshift and take the hill or load at a higher rpm where the ignition advance is in its proper setting, and avoid pinging.
It is very common for Bullet owners, especially Bullets with the 4-speed gearbox with it's large ratio gap between 3rd and 4th, to not want to downshift when they should, because it causes the engine revs to go pretty high when they do. It's better to slow down a bit and take the hill in 3rd, than to lug the engine in 4th.
This is a fairly serious matter, because lugging in some cases can cause the piston to seize in the cylinder, and can blow the whole engine.
Just keep the engine operating in a happy rev range, and all will be okay.