It just popped up in my mind.

• You could decorate any room as you like. You don't even need to step out of it most of the times.
• Other people can be projected inside it like Voyager's doctor.
• Also rooms could be much smaller. They only need to be big enough a human(oid) can fit inside.
• In emergency cases most holograms can be shut off to match increased energy demands by weapons and shields. You only really need seating/bed and a (non-exploding) console screen.
• Much of the specialized rooms like a bar, med bay, etc. won't be needed anymore as a holodeck can imitate all of them.

It irritated me a bit that a Discovery gets fancy floating warp nacelles but holodecks are... wait, does Discovery has a holodeck? I don't remember seeing one.