Generation changes are when birth rates show a shift in increasing or decreasing. Usually this is in line with the national economy. Because of globalisation, we tend to see large groups of nations have birth rates shift within several years of each other as their economies are quite intertwined and do the same things. And that's also why people always argue about what year a new generation started. It is different for each country.

Outside of (mostly) economical context, they have little purpose in discussion. And even then, they're more used to refer to an era of economical positive or negative in households, which was reflected in birth rates.

90% of the time people use them in everyday conversation, it's "old" and "new", which can be easily said without mention of generations since that's how society has always been as time goes on.