>>2116873>>2116867I looked at some studies (i.e. googled it, clicked some PDFs and scrolled down to see the pretty graphs) and they seem to suggest there is often some benefit, but sometimes none or limited benefit. This one shows that the inoculant is more effective in greenhouses (presumably because the strains you can buy are not as well adapted to hard outdoor life) but also somewhat effective outside and that other techniques like "shortened fallow" (I guess that means cover crops) are also somewhat effective.
Another one showed that a few untreated grape vines acquired fungi of their own accord by the second year, but most had not. Interestingly the location where none of the untreated vines acquired fungi on their own also showed the most benefit from treatment, so I wonder if the soil there was just dead and at the other sites there may have been different fungi species that wouldn't have shown up in the testing.
In conclusion, it may help or might do nothing depending on your situation, but probably won't hurt. There may be some truth to it giving a "head start" compared to waiting for the fungus to grow naturally.
