I remain surprised and impressed by Ubisoft's long-term committment to Tom Clancy's Rainbow Six Siege [official site]. As part of the 'Ongoing Health' chain of tweaks and tune-ups, they've announced plans to optimise all maps, including going over textures and replacing skies. They want to make everything run better, see. They've starting with the map Kafe Dostoyevsky, which should be live soon-ish, and will continue on others over the year to come.
Here's this on tidying up textures and meshes:
"Over the course of the next year, we will be reworking the textures of every single map. We are starting with Kafe Dostoyevsky, our most expensive map in terms of memory-budget. We have been going through all the textures and meshes of Kafe, smoothing, optimizing, and standardizing everything we could. In essence, we are streamlining and reducing its overall memory footprint. [. . .]
"This is a first milestone that will allow us to optimize stability and frame rate, while maintaining visual quality."
As for skies, Ubi say that Siege will switch to using HDR image skyboxes. They had borrowed some procedurally-generated sky technology from Assassin's Creed, but that proved slight overkill when each map is only ever seen at two static times. They say the new method "allows us to have more artistic control of the ambient lighting, as well as increase the overall quality of lighting in general."
Meanwhile, they're tweaking lighting to be friendlier to players. Specifically, the exposure effects which make it hard to see through a hole into a place with different brightness. Holes to lighter places won't be blinding white, to darker they won't be inscrutable shadow. It's less realistic but they say it's what players want.
Anyway. There's more but I won't repeat everything. Go read the blog post for that. Another two posts on other optimisation efforts are promised.