[Unkle Krusty]

A study of a horses lower leg will reveal the answer. Less un-sprung weight.
Einstein said it requires energy to move mass, and the amount of energy is in proportion to the mass. If the lower forks weigh more, they require more energy, to move them up and down. Energy in action creates heat. If you want very fine control over the movement, less weight helps. Move your mouse. Move your full coffee mug. Einstein is right again.

UK

 

[Unkle Krusty]

The rest of the theory, as the article at the link says, is that unsprung weight is reduced, resulting in better damping and control. Looking at photos of inverted forks, I wonder if there is really that much difference in moving mass. I've read that 1 ounce of usprung weight equals 7 ounces above the springs for damping control, so a little weight loss could help, I guess.

You managed to just get that in before me.
For street riding I do not think it is necessary. Bluzu has normal forks and are more than good enough for the street. I think for very quick track riding, at the top of the leader board, there will be enough difference.

UK