[kimixa]

In British English you'd be wrong for using an em-dash in those places, with most grammar recommendations being for an en-dash, often with spaces.

It's be just as wrong as using an apostrophe instead of a comma.

Grammar is often wooly in a widely used language with no single centralised authority. Many of the "Hard Rules" some people thing are fundamental truths are often more local style guides, and often a lot more recent than some people seem to believe.

[optimalquiet]

Interesting, I’m an American English speaker but that’s how it feels natural to me to use dashes. Em-dashes with no spaces feels wrong for reasons I can’t articulate. This first usage—in this meandering sentence—feels bossy, like I can’t have a moment to read each word individually. But this second one — which feels more natural — lets the words and the punctuation breathe. I don’t actually know where I picked up this habit. Probably from the web.

[evanelias]

It can also depend on the medium. Typically, newspapers (e.g. the AP style guide) use spaces around em-dashes, but books / Chicago style guide does not.