When does this actually matter though? Isn't growth (or shrinkage) what you'd normally really care about (e.g. this month we had 10% more DAUs than last month)? I suppose if you changed something to attract tons of new users who disproportionately use AdBlock (for example) this becomes an issue as it wouldn't show up in your metrics, but is that sort of thing common?

I suppose if nothing else it's good to know so you can immediately beef up your numbers +20% in your slide deck for VCs.