When I was young, I usually saw English written in a relatively sane way. Parts of a sentence that fit certain semantic criteria would be separated from the continuing sentence by
- on both sides, while compound words separated their components by
- - with no spaces.
But nowadays, something terrible has happened. People usually don't put spaces around their dashes! They write things like "I picked up the weight-which was hard-and carried it to the destination"!
There's a reason we did that! There's a difference! If you don't put spaces around your dashes, they're easy to confuse for hyphens! This can waste entire seconds of every reader's life, so I had to spend like fifteen minutes of mine writing this! You are responsible for this loss of mine, reader, if you misuse dashes. You can thank me for setting you straight if you wish.
Sometimes they use bizarre mechanisms to "distinguish" like the Unicode en dash and em dash.
Never use the en dash or em dash because they are not ASCII characters, and therefore are a chore to type in most environments and can cause compatibility issues, and do not do anything that ASCII characters can't.
Go, writer, and commit no more the sins of misused dashes. I am without this sin so I can throw a stone at you.