What you need to know
A fixed font size can be too small on a phone or oversized on a wide screen. clamp lets you choose a lower bound, a flexible preferred value, and an upper bound so typography responds without a long list of breakpoints.
How to apply it
Start with a readable minimum and a comfortable maximum, then tune the middle value with viewport units. Test real headings on mobile and desktop and watch for awkward line breaks.
Common mistake to avoid
Do not use an unbounded vw value by itself. Text can become tiny or enormous when the viewport is outside the screens you tested.