I have been at restaurants where “fancy” waiters pour wine with 3 fingers under the bottom of the bottle and their thumb in that dent. It looks elegant.
Another thing - the indentation makes it very easy to cork the bottles - the corker has purchase on the bottom of the bottle, so it doesn’t slide when the cork goes in.
Not that Cecil is wrong or anything like that.
Cecil calls the dimple a “punt”, but IIRC the correct glassmaker terminology is “pontil”.
According to the Oxford English Dictionary, a pontil is a glass-making tool, and “punt” means the indentation, but also sometimes means “pontil”. It doesn’t say that “pontil” sometimes means “punt”.
Righto! Wine bottles with contured bottoms are much easier to pour from.