I read that graph differently where doing the work + more/extra/nothing is your 8h day. And so if you do the work + any of these it will amount to 8h. If you do nothing, you’ll still be stuck at the office anyway because if you do the work and leave early you’ll be asked to do more since you have leftover time. You won’t get to spend that time on your family.
If you're working from home and getting your job done to the satisfaction of your employer in six hours, I think you can do what you like with the extra two hours. You may need to be available to your coworkers, but the rest is up to you.
I think doing Extra, More, or "Nothing" are all fine choices, if by "Nothing" you include spending time on family, community, health, and non-professional education. For professional advancement, I think "More" is a fine choice if you have good management. Management should have the perspective to appreciate you making the right choice for the business. If they don't, well, in that situation, I find that advancement depends on selling yourself to people who only care if you're delivering good news for them and can't appreciate anything else.