>>723733945 (OP)
>Is an extra 100% checklist on top of the in-game list.
>Usually pushes you to do things you might not want to do like higher difficulties or challenges causing you to see more of the game or experience more of it than you naturally would have without them.
I would have never touched Proud or Critical on Kingdom Hearts without 1.5 and 2.5's trophies. Now I only play on Critical.
>In some games it can work as a way to mark progression through a game and note what is coming up next to prepare for.
This specific point is more for RetroAchievements as they have their achievements ordered in when they would be achieved during a playthrough instead of randomly grouped together.
>Gives you proof you did something which greatly helps when discussing or arguing certain things about a game.
They don't harm anyone, they're fun to go after most of the time, and as long as you're not the kind of nutjob who buys games only to get achievements in them or avoids games because they don't have achievements they're not really doing anything to you. If they bother you that much you can always turn their notices off, and it's not like it takes much effort for devs to add them either.