It’s down to common sense really. Yes if you aim the tip of the lance direct onto joints you risk the “possibility” of causing water ingress.
With the lance kept at a distance the pressure is greatly reduced i.e. no greater than rainfall whilst travelling on the road.
I’ve been using pressure washers for 50 years and to my knowledge never caused any leaks.
I once passed the lance directly over my hand while washing an item and holding it at the same time. Yes is does sting a bit. !
