There are links to published scientific studies at the bottom of the Wiki explanation. I am sticking to science.
The Mycorrhiza doesn't create the roots, it does help the plant absorb everything faster (yes, water too. I can attest to that), but it also helps with better colonization. Kind of like a forman at a construction site doing a better job than the last foreman (best definition I can come up with).
I'm not sure how it helps the roots absorb more of everything. I haven't done enough research to answer that yet. But as I understand it salts build up when there's too much of the nutes for the plant to absorb (when nute burns occur), and a build up of salts is what causes lock outs. I'm not really sure if the build up of salts are a bi-product of the nute burns, or if the left over salts are simply what the plant can't absorb causing the build up.
All I can tell you for sure is with all the problems I've had (soil that was too hot causing occasional nute burns, underwatering, 3 infestations, heat problems, pH problems & 1 fluctuation, no folliage feeding due to the 24/0 light scedule, etc...) I would be lucky to have 16" plants right now without the Mycorrhiza. And I didn't even treat for the first time till I was into the 3rd week.
My next grow I'll treat from day 1 and as long as I have less problems, which I probably will, I should have close to 3ft plants by the 8th week. I may also need 15 or 20 gallon planters as well, but the extra yeild should be worth the trouble.