My two cents:
In open-world games that allow you to go anywhere right away, scaling is bad news. If the game allows me to storm the Big Bad's castle at level 2, that's fine. My little adventuring party should get totally eviscerated, though, to let us know just how much better we're going to have to get to succeed.
Most games circumvent this by giving the player a not-so-subtle push toward quests/assignments more suited for their level, i.e. "Oh no, my basement! There are rats everywhere!"
Would you rather have a system in which if you skipped that particular quest and came back at level 20, and those rats were able to give you a hell of a fight? That does not make sense!
In a more linear game, however, when the designers have more control over the types of enemies the player faces and when they face them, scaling can make for more balanced gameplay. I'm cool with that.