https://passionford.com/forum/general-car-related-discussion/172925-who-uses-engine-flush-when-changing-oil.html

this thread comes up at the bottom of this one.good reading methinks.

however, I reckon if you drive normally then once in a while or frequently give it a booting the engine should be relatively healthy. at my dyno session it hit the limiter 3 times and there was a shitload of black soot deposited on the tailpipe. so as long as it is driven well, good quality oil used, changed frequently enough shouldn't be too much of an issue.

quite a few stories of how engine flush fucked an engine up in that thread too.