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Thanks Kate, 
the  https://s3.amazonaws.com/images.seroundtable.com/hreflang-google-mobile-first-1511959807.png is really what I needed. Cheers!

I have a client with a site with a m-dot mobile version. They will move it to a responsive site sometime next year but in meanwhile I have a massive doubt.

This m-dot site has some 30k indexed pages in Google. Each of this page is bidirectionally linked to the www. version (rel="alternate on the www, rel canonical on the m-dot)

There is no noindex on the m-dot site, so I understand that Google might decide to index the m-dot pages regardless of the canonical to the www site.

But my doubts stays: is it a bad thing that both the version are indexed? Is this having a negative impact on the crawling budget? Or risking some other bad consequence? and how is the mobile-first going to impact on this?

Thanks