What does "include games from my collection" mean on the next achievements page?

The title. I have no idea what it changes.

In your Collection, you may have games that you haven't started yet. So if you want to see 'next' achievements for those games as well, you can check the box. Else, the overview will only show next achievements from games that you have already started (unlocked at least one achievement means 'started')

Oh that makes sense, thanks