What programs actually use the memory on a Graphics card? I noticed that the Graphics Card memory is hardly used at all, even during Cinebench 3D testing despite the FPS being high. What programs actually use the graphics card memory?

Trying to determine if the M295x is worth the money to upgrade in a new iMac. (I do mostly video editing with Premiere Pro and After Effects)

Currently running an iMac 5k with the M290x card.

Here's a screenshot running Cinebench 3d test - high FPS, no GPU memory being used...
3D games do. In fact, they often use lots of it, which is why you see cards with many gigabytes of memory these days.