When you need to make something seem important, bold is the right choice.

You can use italics for foreign words like the Greek týpos — “reflection, form” and gráphō — “I am writing”, which together form “typography”.

Underlined text should be used with extreme caution as it stands out a lot.

Sometimes you may need to mark text as deleted. Strikethrough is the right choice then.

If you write about software, the option to mark inline code like printf("hello, world\n"); comes in handy.

There are also _subscript and ^superscript types that might be useful in texts about chemistry or math where you have to deal with things like H₂O or x².