The useful burst is short: press, release, look at what moved, press again. A second or two is plenty for most of what a duster is pointed at, and the pause between bursts is doing as much work as the burst.
Holding the trigger down feels more thorough and is not. The can chills, the pressure falls and the last part of a long hold is weaker than the first part was, so you are spending contents on a stream that has already stopped being good.
Dust moves in the first fraction of a burst or it does not move at all. If a second of stream did not shift it, four seconds will not either, and the answer is a different angle or a different tool rather than more gas.
That is the single most useful habit to build. The stream is not a pressure washer, and grit that is stuck is stuck for a reason a cloth usually understands better.
Fit it whenever the target is narrower than the nozzle is wide. Between keycaps, along a heat sink fin stack, into a bobbin race, down the gap between a panel and its bezel, inside a port. In all of those the wide stream mostly goes past the thing you were aiming at.
Leave it off for open work. Fan grilles, the floor of a case, a shelf of models, a set of blinds: those want coverage, and the straw turns a useful spread into a narrow line you have to trace by hand.
Point the straw down the length of a gap rather than into its face. A stream that runs along a seam carries what is in the seam out the far end. A stream fired straight at a seam pushes it deeper and packs it.
Same idea on a fin stack: work from the back so the felt leaves the way it came in. Blowing into the front of a heat sink turns a loose mat into a tight one.
It is a thin plastic tube on a bench full of thin plastic things, and it goes missing constantly. Clip it back to the can the moment you finish rather than setting it down, and it survives.
The straws are interchangeable across the sizes, so one from an old can fits a new one. Worth knowing before you decide the new can came without one.
Dust-Off