> Even if everyone eats a perfect portion for themselves, if you overestimate the total then you'll have food waste if the food can't be preserved.

That'd be just poor planning on part of the hotel/restaurant. It'd be a valid excuse when starting new, but after a few weeks that should be under control.

If you only do breakfast buffets it's a bit harder - but you monitor the situation, and as breakfast time approaches the end you reduce things you can't store or re-use otherwise. Pretty much any hotel I've been to in the last few years had that kind of items run out without restocking them when we had a late breakfast.

If you also do lunch/dinner buffets you have some more options, and can have some dishes reusing the leftovers. I've also seen that regularly - they had the planned dishes, and a few smaller pots with something they came up with to reuse whatever was left over.