Scroll wheels and zip codes
A customer was charged for 40 of something they had ordered 4 of, and the mechanism turned out to be a browser behavior sitting inside the one input type everybody reaches for.
fieldset and legend
A group of radio buttons has a question attached to it, and the question needs to be in the markup rather than in a heading that happens to sit nearby.
optgroup
A select with 40 options in it is nearly always a select that wanted three or four labeled groups, and the element for that has been sitting in HTML the entire time.