(I don't have all 10 so I'll start the list with the ascending order)
1. There's no incentive to cheat
2. You can always pretend that your opponent is Carlsen
3. Finding matches is much quicker
4. If your opponent is losing and goes offline, you can just start another game
(insert your own reasons)
It's just for the chess, no point of ratings.
I guess we can give contrary reasons as well:
1) You can't check you opponent strength and you can't play accordingly.
At certain level, you don't play the same against diferent skilled players. I do not make the same moves against 1800 players, than 2000, than 2200. And this is fun as well, whereas if you don't know your other player strength, you can't simply imagine it because your opponent will not play accordingly and it will not be fun.
For that reason GM like playing Simuls against lower player.
2) Ranking its just a number and it doesn't represent nothing; and ranking points online its even more useless, but its usefull for your own because you can see your imrpovements.
3) You can have a track of your games.
4) You can check other high player games against other higher or lower opponents.
5) There may not be incentive to cheat but people can cheat more easily because you can't banned
Click n play, no sign up, no bs. Lichess#1
5. Zero stress
6. You can resign a winning game as a sign of triumph
7. No distracting chat when you're trying to think
8. Higher rate of participation in non-standard formats (960 etc...)
9. You can ask for takebacks
10. It rhymes with "mouse"!