It's been decades since I used this procedure. I can't really say whether it's something that will "extend" the life of a motor or not but It does appear to remove carbon deposits. One thing I would be concerned about is carbon "chunks" getting caught in the exhaust valve when it closes and getting a deposit build up trapped on the mating surface. This would prevent an exhaust valve from fully closing. So I guess it's a hit and miss thing unless you do it over a long period of time and the engine is running fine at idle when you are done.
When I have done this, I have had control of the pedal and my RPM is up fairly high while I'm injecting water. So far, so good (fingers firmly crossed).
Again, I haven't done this since I was driving $75 beaters ($750 in todays market. Just for you coasterII. Oh, BTW coasterII, I played in a working rock band for 30 years, You'll never get the variety of skank I've had. Keep dreaming that you're the man

). You may be younger but that will fade. My weight, ya, it caught up to me because of life altering injuries but I can diet and can probably bench press more than you. You can't fix stupid. I'm still waiting for you to prove me wrong about you by actually fixing something.