ZZman said:
I guess it is this:
A high-pressure cleaning solution is attached to the fuel system at the engine. The technician runs the engine exclusively on the cleaning solution which breaks down carbon, grime, and debris build-up on the fuel injectors, and washes any deposits from the rest of the fuel system.
The high pressure injector cleaning may be necessary on a car that has over 100k miles on it and was run with the cheapest non-top tier gas available most of it's life. But adding a bottle of Techron or other quality fuel system cleaner for a few dollars every 5000 miles would probably obviate the need for an expensive dealer service. A 2017 vehicle with 78,000 miles on it probably didn't need the dealer service, provided that they even did the high pressure service and didn't just pour in a bottle of cleaner.