some writers tend to better when they have limits placed on either by themselves and sometimes by someone, it keeps them from going too bonkers and dumb in a bad way.
Honestly, a lot of writers write better with a limit of some kind. I mean, even One Piece, a series where literally anything can and does happen, has fairly solid limits and milestones that need to be hit.
There's something to be said for laying out even the vaguest milestones for oneself. It's always the series that don't have them or abandon them that go off the rails.