I have a Karcher in the garage that is rarely used.
To me it seems a lot of effort getting the thing out and untangling the hose, running the hosepipe out and then the mains cable and connecting it all up. (It's all to be put back again afterwards)
It will clean paving slabs, but in narrow strips which gets tedious over a large area. With my block paving it forces the sand from the joints.
It's too powerful for the caravan, forcing the mastic out of the seams, but is OK for quickly applying a detergent from a distance.
All in all, I don't consider it particularly labour saving.