A application of Berryman Chemtool once every three oilchanges to flush out the Junk from your engine will make you e engine go for 300,000 miles ( if you have a 22r toyota engine like i do).
There are many 22r engines that have gone just as far without chemtool, and many other engines from different makes that have without any kind of flushes as well. Generally, if you change your oil every 5k or so with dino and your engine isn't sludge prone, it will last. There is another thread that had many peoples examples. Maybe someone else can find it, I can't at this time.
I fully agree with Schism.
The trouble is, there are far too many men unwilling to take proper care of their motor vehicle.
For them it is RX, ChemTool,Preen, etc, and/or short engine life..
I could do a better job myself, admittedly; as I change the oil every 4 to 6 months(2 to 5K miles).
Never use any flush anywhere, except at the toilet...lol