The worry is wear does anything that's dislodged end up.
For example when I'm cleaning pistons, I take them out and soak them to remove any build up, after a few hours what is left is a sticky mucky residue in the bottom if the bucket - now if you get the same affect with a flush and that stuff gets pumped around the engine - not all of it is going to drop back into the sump .
Regular oil changes are the best thing in my opinion. I have a theory on why manufacturers no set service intervals to 18,000 with so called long life oil - ultimately it will lead to engine failure at around 150k - meaning they can sell more cars - open up a modern engine on 100k that's had 18k changes and you can see why .