On average twice a year I clean the filters in the underground irrigation sprinklers, four of them.
Perhaps double of that number of times I cut away the groundcover around the sprinklers.
In addition the filter on the water-inlet hose gets cleaned once, in the beginning of the year, prior to switching on the garden-pump for the first time.
If the filters are filthy, too little water gets through and the mechanism will not be able to lift the sprinkler to its maximum height and not have enough power to let the sprinkler turn at all or not at the desired speed.
Related: Preventive maintenance and repair, Watering supply and irrigation or sprinkler-system, Constructing the Infrastructure.
You are vigilant, I don’t think I’ve ever cleaned our sprinkler system, or trimmed around them at all! They still work great though. When we got our sprinkler system I did about 3 months research to find the most efficient one while staying within our meager budget. We settled on Orbit Irrigation, really great sprinkler systems, check out their website here: http://www.orbitonline.com/sprinkler-systems/02/