Pressure washers can blow the rubber out of o-ring chains. Ditto for all the little rubber grommets, covers, isulation, wire connectors, etc. They can also be directed to reach into areas not intended to hold water (such as your airbox, which is a bit harder to accomplish with a garden hose..
That said they're a temptation/ worksaver after a long offroad trip. Use them gently and sparingly with with a fan pattern, if at all.