@cheeseberry I thought he had something more specific, but right now I'm just finding this post with screenshots and his response right after: https://forum.faforever.com/topic/1186/ui-mod-guide-for-the-improving-player/10
The detrimental part is seeing how many low level units are in a clump early game. In higher level ladder that's really important. That being said, I'm not really sure exactly how detrimental it is to being able to count small numbers of units if you're using the small icon sizes. Not sure what size is being used in the screenshots here.