Most of the work we do is in single family homes or attached villas.
Every home that has a dryer vent needs to have it cleaned out from time to time.
Our recommendation is as follows:
one or two people, every 2-3 years should be sufficient.
three or more people, every 1-2 years is usually ok.
if there are pets that shed, or young children in the home, then the vents should be cleaned every year. The reason is because animal fur clings to the moist lint in the dryer vent and will cause it to clog much faster. And having Children in the home causes faster clogging due to the new clothing releasing more lint and the excessive machine use.