Postprocessing uses too much VRAM
Since postprocessing feature was added to OpenMW, it started to use an additional video memory, even when postprocessing is disabled (it is about 600MB on my setup in some scenes, with total usage 1.6GB in 0.47 and 2.2GB in 0.48).
Such additional usage may make OpenMW unplayable on devices with low amount of VRAM (1 or 2GB) when mods with high-resolution textures are used (and there are complaints on Discord about it). Basically, when there is not enough memory, OSG tries to unload textures every frame to avoid OOM crashes, what causes a large performance drop.