Some of the video game ratings here used to include a more detailed summary of the content, with meters indicating the level of language, violence, sexual content/nudity, etc. in the game, making it easy to decide if a game had too little or too much of a particular category of offensiveness for one's tastes. These days, though, all I see is the unhelpful letter "M", or maybe the occasional "T".
Those letters are helpful in making the snap decision as to whether to even bother investigating the content further. I can't give every game/book/movie/whatever proper review, so it helps to know that some sane adult marked it with an easily-understood cue. If there's an "M" or "T" on the box, I don't want to waste another second wondering if it's suitable for my toddlers.
Example: "Happy Tree Friends" is advertised & starts with cute forest animals in simple & colorful renderings; an appropriate parental cue helps prevent having to explain other definitions of "rendering" to a kid who can barely talk and is wondering why seconds later that cute squirrel is shrieking, spewing red, and has a bad case of the ouchies. A prominent "T" would be helpful to those adults who don't know the show and are being pestered by a 3-year-old to watch it on Netflix.
True, an indication of recommended age may help in the Happy Tree Friends case. But I think some 10-year-olds might also not like it very much, and they are teens already. If it said "strong violence", that probably works even better.
Of course the best thing is watching a trailer on Youtube, but you can hardly do that for every series the children ever watch. This is more realistic with games, at least until they start buying or downloading their own games.