You have seen many big websites like Facebook and amazon were already offering mobile version websites to there users that are browsing from phone.
But after mobile friendly Google algorithm update, almost each and every website is now displaying mobile version of websites to there users who are browsing from phone.
Even SolveMyHow shows mobile optimized website to their users.
Why big companies and bloggers are moving towards mobile optimized sites ?
I'm mean there must be a strong reason behind doing this right. Let me tell you the reason. The first reason is Google algorithm update.
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So from March 2015, the sites which are not fully mobile friendly will be penalized by google and people searching from mobile will be given mobile friendly sites first. So obviously if amazon's site is not mobile friendly then other eCommerce company would have been shown in the mobile search results.
P.S this won't affect when users is searching from desktop. So you only need to worry about this when you want traffic from mobile sites.