Behind the scenes, Snowdrop aims to utilize 75% of your dedicated video memory (VRAM), leaving space for other GPU-accelerated, memory-consuming apps that may be running the background. Within this 75% block of memory, which may be exceeded, memory is earmarked for any settings you've enabled that use VRAM, and the rest divvied up between geometry, other necessary game elements, and textures required right this second. Any remaining memory is filled with additional textures for nearby areas, reducing the chance of pop-in and visible streaming as players travel through the world.
As such, users of GPUs with less than 6GB of VRAM may not receive maximum-quality textures at all times. Whether you do or don't is based on the selected screen resolution, the detail of the current area, and the quality selected for the many game settings.
If you do somehow fill your GPU's available VRAM, perhaps with a high resolution and max settings on a 4GB GPU, The Division will do its best to scale back detail to rectify performance. In some cases though you'll have to step in and dial back the aforementioned settings, or the resolution.