52% of users are less likely to engage with a website with poor mobile experience

Whilst standard computer screen are conveniently large, mobile phone screens have minimal space. Failing to consider different screen sizes isn’t good UX practice, and may result in a website becoming increasingly difficult to use on a mobile device. This presents a strong deterrent to users.

Source:
https://www.thinkwithgoogle.com/advertising-channels/mobile-marketing/what-users-want-most-from-mobile-sites-today/