When you turn on your garden hose and turn it to the jet position, have a look at the size of the hole the water is coming out of, Town supply water is usually about 100 lbs pressure.
We had the same quantity of water, pressurized to 3,000 PSI, coming out of a 1mm hole.
I have buckled the sides of steel fishing vessels while water blasting the barnacles and growth off the hull.
I haven't, but I have heard that they use high-pressure water to cut steel sheeting to patterns, cheaper and easier than Oxy/Acetylene torches.
The longest part of clearing roots was to find them 100 meters up the pipe while working by feel. you could tell how you were going by the debris that was washed down the pipe.