I think if you report someone who plays shitty for Griefing/Feeding, then another player will review the replay in the "Overwatch" program, and if he has some common sense he would confirm that the person was griefing/feeding.
In Overwatch mode i've never reviewed a person reported for communication abuse, and i think thats because they just scan the game chat log for bad words from a list they compiled, and if they find any they issue a temp ban/low prio? could potentially backfire tho, not sure.
What i think has the biggest potential, is if you go to the persons steam profile and report him, there is alot more options and you have a chance to explain and provide evidence, screenshots etc. Lets say i trigger someone so much in a game, that he calls me the N-word, or make threaths about violence/death. You screenshot that baby, i would assume you have hes ass on a plate, because those are probably zero tolerance topics.