We will never see movies with large numbers of extra used again??

Why not? How many reasons do I need. Aside from training, discipline, costuming, set and setting, etc, you have the financial reasons.

Labor laws, minimum wage, health insurance, retention guidelines, injury liability, etc, all come with costs so, there are soooo many purely financial reasons to digitize the Roman army rather than hiring them that, barring a very compelling argument made to someone with very deep pockets, you're probably going to use virtual background characters at least.

Just think about the cost of reconstructing the fortress of Mordor and then ask whether you want to digitize THAT. Then think of hiring an army of orcs and ask the same question. All of those kind of big FX make virtual stuff more likely.

You probably do not need to digitize Jerry Seinfeld's apartment and its four main characters, but the bigger the scene gets the more likely you will. It's a matter of cost and time.and how long it takes for the bean counters in the company to figure that out.

Y'all realise that even before CGI, filmmakers looked for ways to make it easier/cheaper to film scenes with large numbers of people, right?

Remember those shots of the Emperor walking down the hangar of the Death Star in ROTJ? Most of the stormtroopers were part of a matte painting.

Smart filmmakers will ALWAYS look for shortcuts to make shooting easier/faster/cheaper - they'd be stupid not to!

There is a big "yeah but" there. Our expectations for movies, especially FX extravaganzas have gotten so high that a matte painting just won't do. Stormtroopers who don't move won't work.

A lot of the digital stuff IS a way to work the easer/faster/cheaper formula. The scary part is when the entire movie is digital.

I thought I was merely noting how we were in agreement.

The stormtroopers in that scene are supposed to be standing at attention, no reason they should make even the slightest movement

Maybe one moment would be practical, but once those storm troopers start to move, it becomes an animation task, not to mention that no human, even a Marine, can stand still without moving for very long. It ceases to be believable.

Flashing back on the LOTR armies, one of the things that made that work so well was that, at least some of the close-up orcs, elves and humans in those big battle line-ups, did small movements, breathed, grunted, expelled vapor breath, etc. They were not just painted sets. You have to have movement in a scene like that or it just doesn't work. The back rows of orcs might be static, but the ones up front have to move and act alive.

They are in the background.... you're barely supposed to even notice them.

What we will probably never see again, however, it something like the 1950's Ben Hur, in which a prop arena was built and stocked with extras, cheering on charioteers who are driving real horses. Those sets were seriously impressive. The whole doggone thing was an amazing sequence. The "extras" were both equine and human. Animal rights people would go completely ballistic, medical expenses for cast, especially those poor fellows who get trampled by the horses, would bankrupt the studio.