Make it Big sites strike me as a misinterpretation of “mobile first” as “mobile only” and, as several of you have commented, it’s easier and less costly up front to use one design. But the downside in user retention on larger devices could be even more costly. Just a few days ago Nielsen Norman Group published an article on why the page fold still matters (http://www.nngroup.com/articles/page-fold-manifesto/). Big is super for some sites, but definitely not for all.