Considering vinegar is flavored water (when it says 5% acidity it means 5% acetic acid diluted with 95% water) you are using water, or in other ingredients as well. And if cooking a long time it can be useful if you are cooking down and don't want to add any other flavors or sweeten. Cooking down from thin to thick with water can richen all the flavors. And the water evaporates so you are not using it, but if you used pineapple juice the sugars would be left behind. Water is the #1 neutral ingredient, don't be skeerd.
Bingo. Carrots, juice, and all this stuff, people forget good sauces can be simple. Scared of water, and even vinegar. I'm also a "pepper sauce" person. I like all sauce types but a lot have limited uses.