<header>…</header>
header {…}
is slightly shorter than
<div class=header>…</div> .header {…}
is slightly shorter than
<div class=header>…</div> .header {…}
Although, any example that I could provide that would show the exception would also likely be a special use example. So it turns into a your mileage may vary situation.
But, I've not always seen a slightly shorter amount of typing as a benefit to this sort of thing.
<main role="main">
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