Vinegar has numerous health benefits, it can help boost immune systems, and in chicks and chickens helps stressed birds immune systems regain strength. You can use regular vinegar though apple cider vinegar is believed to have more health benefits than plain.
If you add it on a regular basis to your chickens and chicks water, it has added antibacterial qualities that help keep your waterer from developing fungus growth.
People can take it too, many use it during a cold to reduce phlegm and boost individual immunity. It is especially effective in aiding recovery from respiratory infections.
Worth buying in the big size you can use it around the house to make your towels fluffier and more absorbent (it removes detergent build up that makes towels less effective), cleans almost everything, and when added to pie crust evaporates during baking to leave it flakier.
Really there are tons of uses for vinegar. You can find recipes for making your own apple cider vinegar on the internet. You can make big batches up cheaply and it uses apple rinds and cores that would otherwise go to waste. If you don't eat a huge amount of apples you can freeze the cores and rinds until you have enough to use and then defrost when ready.