With manufacturers using more fins/inch to try and get max efficiency out of system it is tough to get the embedded dirt, pollen, and debris out without using a foaming coil cleaner. The only issues that I have seen is when people do not rinse the coils well enough to completely remove the coil cleaner. Especially at the tube sheets.
Oh, and with Micro Channel coils (ie. fancy name for radiators) they DO NOT recommend any coil cleaner just water. A step forward equals two steps backwards. But when you have engineers coaching a game they never played, this is what we get. I know EVERY service tech ALWAYS carries a pressure washer up his ladder.