A very short answer would be - it's undefined. It depends.
I've learned a lot from games - I've learned English, Ethics & morals, and I've learned school topics before I even had to. They can be both harmful or beneficial to your knowledge. It all depends on what game, when, and all these kind of things.
They can be for pure enjoyment & fun, or for teaching and learning. I myself like playing Multiplayer games similar to DayZ and other kinds of games in which ALL choices matter - and nothing is ever the same. This way, even if it's through a game or not - I deal with several situations and many ways different people can act - whether they say "I'm friendly!" or they just instantly try to kill you. People lie, people say the truth - in the end everyone's different - some people the same in reality & the computer, some different. I've learned English and some Russian & Japanese from games. I've learned many words, I've learned to illustrate and lots of other things. It just depends on how you use them and how you look at them - how you play them, and how they're meant to be played. Many ideas can flow in and out of a game, but they will always be variety, lots of variety. It depends on the age and on your knowledge & behaviour prior to these games aswell.
It's kind of a difficult topic but - to me, it all depends; on the game, yourself as a person, and at -what- time you play(ed) such game(s).
Some often do some behaviour inducements with what we'd call "achievements" but as long as these stay within the lines I believe it's OK. Some people've got to understand some games are a joke and that some are real.