Which of these uses are real and which are just someone flapping their jaws?
Vinegar as an herbicide: White vinegar which is about 5% acetic acid and does a nice job of burning the tops of plants, but not their roots – so a larger weed will live right through a spray even though it will look bad right after the spray. You can buy 20% acetic acid. It works faster, but it has essentially the same problem killing larger weeds that that 5% acetic acid does. Besides efficacy issues there are safety issues also. I’ve used 20% acetic acid and I think that this stuff is too dangerous for the average person. A little in the eyes could cause permanent injury. Just a little whiff of it is enough to make the nose start running (in other words it’s not good for mucous membranes).
Vinegar as a disease control: What a great idea! Spray something that kills plants onto your prized petunias to control disease! OK, when you use vinegar as a plant disease control you do use a lower concentration which shouldn’t hurt the plant. But vinegar has never proven to be particularly effective at controlling plant diseases.
Vinegar as a fertilizer: Nope, doesn’t work. Acetic acid only contains carbon hydrogen and oxygen – stuff the plant can get from the air. The other things that may be in vinegar could be good for a plant – but it seems an expensive method of applying an unknown amount of nutrition.
Vinegar as a soil acidifier: This is one that I’ve seen a lot – and so I tried it. In a nutshell, it just doesn’t work that well. It takes a lot of vinegar and the pH change is brief at best. Use something like sulfur instead.