First off, throwing a LUT in there is not color grading!!!!!!!! People making this claim are appreciated as it lets me know immediately that they are not familiar with the subject at all. It's like a shibboleth. Edit: I mean this in the nicest way. It's just a pet peeve of mine. You already stipulated you didn't fully grok the topic.
In a full color grading session, you can have power windows. You can have those power windows tracking. You can have noise reduction. You can have other filters. You can do so so much. All of that takes up memory. You can be dealing with 8k footage. You can have many many many layers of that footage. You can be grading in >16bit color space.
You can do all of that with very little VRAM at a snails pace, or you can do it in real-time with all of that VRAM and keep the client in a supervised session happy. With all of that VRAM, you can export at faster than real-time for delivering the content to the client at the end of the session rather than the next day after an overnight render.