I don't let the vacuum nozzle come into contact with anything inside the PC to avoid bending, smashing anything dainty and, also, to avoid static shock.
I use the duster spray to unstick any dust bunnies I find for the vacuum nozzle to suck up. I do hold the nozzle right up against external sides of cooler/exhaust fans but I don't mess with any of the heatsink fans that way. I use the duster spray on those while holding the nozzle opening at the receiving end of the spray jet.