What happens when you spray any plant with vinegar is that the leaves the vinegar contacts will die. Whether that will kill the roots depends on the plant and how often the plant gets sprayed. If you keep the plants leaves dead eventually the whole plant will die because there is nothing, no leaves, to manufacture the nutrients the plants roots need to survive. So spraying even a very hardy plant often enough with vinegar will kill the roots too.

I used Vinegar to deal with weeds. At $2 for a 2 gallon jug from a costco, you cannot go wrong. I do not use it for controlling weeds in the landscape so much. Generally I use it where weeds are growing between cracks on pavement, around pool and places like that. Spray the leaves and down into the crack will kill (most of the time) the plant.

I do use it on mulched area's, but usually might have to come back a couple days later. It works though.

albert, to answer your question about the seedlings: applying vinegar once to a very young seedling will kill the plant. They won't have developed enough of a root system to serve as an energy bank. Thus, no new growth to replace the tiny leaves you've zapped.