Take a bottle of wine, for instance. When I was doing my wine training, it was accepted that you would get six glasses of wine from a bottle, meaning the measure was 125ml. More recently the accepted number of glasses per bottle shifted to five (or 150ml per measure) and there is a trend now for still more generous pours of 187ml and even 220ml, both of which I have seen served in bars.
Now, there may not be a huge difference between 125ml and 150ml in the great scheme of things, but when you factor in the alcohol strength of wine, which has also risen markedly since the early 90s, the differences are substantial, especially if you are watching your intake.
It can be tempting to overdo it a little with spirits, too. I have never met anyone who poured a reasonably standard 30ml measure of spirits when entertaining at home. Now maybe I just happen to know very generous people, but I think there is a weird effect whereby our eyes reduce the amount that our hands pour in. Regardless, it's better to be safe than sorry when pouring spirits.
I'm not suggesting that we should all suddenly start pouring niggardly measures or weighing out our drinks by the gram. The days of a 15ml measure, or a damp glass, as I call it, are receding thankfully, but there's no need to shoot ourselves in the foot by celebrating with an outrageous measure.