WCAG 2.0 Level AA, Guideline 1.4.4 speaks to the importance of letting the user resize text:

Except for captions and images of text, text can be resized without assistive technology up to 200 percent without loss of content or functionality.

This guideline states that all website text must be resizable (zoomable). This was more of a problem in older browsers from around 2005 where browsers wouldn’t resize text sizes as pixels or points, but that isn’t an issue anymore as all modern desktop browsers will trigger a full page zoom when the user presses cmd/ctrl+ (Pro Tip: If you set your media queries with EMs instead of PX zooming will also trigger the media query).