Receive this email From Google: 'Mobile-first indexing enabled for yoursite.com'?

I recently started receiving these email notifications from Google about certain sites becoming indexed as "mobile first" - and wanted to write a quick post for those who are curious and want more information.

Basically, this is a non-issue and something you can essentially ignore if your site is built using latest, common practices.  This mainly becomes an issue only for sites that are not mobile friendly (e.g. desktop only) - or, for sites that have both a desktop and a mobile site.  For my clients, I've never built a "mobile only" site - I always build proper, responsive websites that are inherently mobile friendly.  For some of my older clients, this may be the push that finally drives you into a modern, responsive (mobile friendly) website.