Dent in bottles

why do wine and liquor bottles (or is it all bottles over 750ml?, even milk bottles?) have a dent in the bottom? Does it serve a purpose?

has it to do with taste, sediment, balance?

My Wag is that it is for structural reasons. The ‘dent’ makes the bottom into an arch, a naturally strong shape. This allows the makers to use less material and acheive the same strength.

I used to work in a bonded warehouse; some of the consignments of wine that we received were packaged in quite thin-walled cartons (and the bottles were upside down to keep the corks moist) - the carton wall was so thin that the neck of the bottles on one layer was able to interlock with the dimples in the bottom of the bottles on the layer below without actually splitting the carton.
Whether this was intentional, I couldn’t say.

…called a punt in the trade.

It also makes them easier to pour, giving your finger purchase on a cold and wet bottle.

Here’s an article by Cecil on this, and a follow up thread.