Disagree. If the party just uses Fly to get over the cliff instead of coming up with an interesting solution, that's kind of boring. It also makes it harder for non-casters to shine.

Second, I don't really like when the world scales with the party. The DM changing the world because the wizard blew all his slots stupidly feels bad. Why even have the choice of spending resources over a long period if everything is just going to scale with us?

Also it kind of sucks when you do get to the big boss and the wizard is tapped out because he's been real loose with his slots