What happens when you give font sizing based on vw? For example the font sizing for this webpage is set at 3vw.
Resize the browser window and notice the change in font size as per viewport width. This create problems on mobile devices, i.e font size becomes too small (can be handled via media query).
Also notice, that nothing happens to font size when you zoom in. Thats because of the font size being set as per View port width.