A lot of people have asked the question since Zack Snyder's Justice League was announced. Why did he need to do reshoots if he said the film was done beyond post-production? Well, as it turns out, while reshoots were done, it was only for two scenes. Speaking with Comic Book Debate (via CBM), Snyder clarifies what those two scenes were, including a brief one featuring Jared Leto as Joker:
“First of all, let’s just clarify, there’s like two bits that I added. One bit that I had really sort of hoped to shoot in post but never got the chance to, and then one scene with Jared. This whole little piece with Jared. The truth is, the rest of the four hours of the movie are really just what I shot.”
Ultimately, it sounds like Snyder wanted to simply add Leto to allow full continuity with the other films that were part of his original DCEU plan (Otherwise known as the "Snyderverse") and really did do reshoots just to make sure he gives fans the full version of what he had hoped to deliver the first time around. But he already confirmed that at least 80% of his original version was not in the 2017 theatrical cut while other scenes were simply reshot akin to how Richard Donner's original Superman II had much of his footage reshot from alternate angles by his replacement director Richard Lester before it was released theatrically. In short, despite the debates otherwise, the Snyder Cut is in fact a very different version than the version Joss Whedon mashed together back in 2017.
In addition, two new images have been released giving clear shots of Darkseid and the original, more sinister version of Steppenwolf that was jettisoned for the theatrical cut but will be used for the Snyder Cut:
Zack Snyder's Justice League is expected to be released on HBO Max sometime in March. Stay tuned!