This all goes back to the age when wine bottles, like other glass products, were made by hand. In that manufacturing process, a wooden stick anchored the bottom of the bottle while the glassblower rotated and inflated the end of the neck. The stick created a dent in the bottom of the glass, which was still soft – thus creating the original depression.
So, is it still there in the industrial era? – some argue that the punt is used for structural reinforcement. Others argue that it facilitates the transport of wines. Wine lovers assert that punt helps the sediment to settle in mature wines. And picnic lovers, say the reason is that it is intended to stabilize the bottle when it stands on a non-smooth surface.
The truth is it’s probably tradition, a remnant from the era when wine bottles were free-blown.