If you live in a warm climate, chances are your grapes develop ripe flavors late enough that the grape's natural acid has been diminished. In this case you should adjust the acid back to what the Winemaker think is the appropriate level.
Like with most things, the earlier you can solve a problem, the better. Adjusting the acid before or during fermentation is better than waiting until after fermentation or ML conversion to do so.
Even if you still need to make an acid add later, it would most likely be a small acid correction, as opposed to a major change in acid and pH.