Answer #1:
Not sure about the details but as far as I know, Discord uses GPU for faster and smoother performance. Pro tip: disable this in case you use your device to play games because there’s been many reports about the frame of the game dropping when it’s enabled.
Answer #2:
I’m not really knowledgeable on this and if I get something wrong I do hope someone will correct me. But after a quick googling it seems to be offloading code from you’re CPU to something that can do it better. So instead of the CPU doing all the work Discord is giving certain bits of code to the GPU because it can do then better. Not sure what exactly it’s giving the GPU though.
Answer #3:
Hardware acceleration is used for highly parallelizable tasks, like rendering, video decode, etc.
These involve repeating the exact or almost same calculation tons of times, with different input. CPUs are by design made for sequential execution, and even multicore CPUs don’t even get close to the raw performance of a GPU when it’s fully used. GPUs are designed for graphical processing which involves a lot of these repetitive calculations, which they drastically speed up by using lots of smaller cores instead of few big ones.