The fact that you can long rest basically whenever is a huge break from D&D's expectations. Namely, the adventuring day. Granted, D&D's adventuring day is hot garbage so I see why they didn't stick to it.

But you're right it doesn't make a huge difference in BG3, outside of the few timed events, but it is a buff.

There are certain timed events where a long rest can change the outcome, so in those cases it's very helpful to be able to prepare if you encounter a situation that you're not ready for.