What's the benefit to all these different tag types that have identical appearance and behavior? I remember the selling point was that they would be "semantic" and somehow used by software to add richness (I guess this would mostly be for search engines?). Is this actually happening? If the web had gone differently and styling was done completely by browsers, maybe these tag types would be more useful, but that's not the way things are.
As it concerns my role, accessibility is the main benefit. They do not have identical behaviour.
A <p> tag will be read out by a screen reader as "paragraph", but a div tag will not read out anything but the text inside. I only use a <p> tag if I want my accessible users to know that this is a paragraph (of a larger body of text).
I suppose you could make similar arguments for the other semantic tags. You use them when the content explicitly matches the intent of the tag so that other software can pick up and read it with a bit of... ahem understanding.
