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.
When holodecks were introduced in TNG, they were presented as brand-new bleeding-edge technology that the characters had never even heard of before. This was reinforced by the fact that they almost immediately got a major update from the Bynars and also had a bunch of weird bugs and glitches to deal with.
Voyager, which was only a few years newer, had an obviously more advanced holographic system, with emitters in sickbay and whatnot.
IIRC, other, even newer, ships had holoemitters all over the ship. Clearly, the technology was rapidly advancing and proliferating in the TNG era.
As for Discovery nonsense, ¯\_(ツ)_/¯