i stopped doing them after realizing that theres sometimes a comeback. a phone call weeks later to tell me theres still a problem( turns out to blocked downpipes ) or "its leaking " and the trouble is unless you are there when its pouring with rain you cant see what is the problem . you could easily be sued if a householder has any damp as you make yourself liable by touching the gutter.
it might seem unlikely but to me the risk of a claim wasnt worth the effort of cleaning gutters . Also cleaning the undersides of gutters is VERY hard work