Moving through text using Cmd + Left/Right arrow will jump over two words if there’s an em dash between them with no spaces. As a frequent em dash user that was very annoying, so I switched to adding spaces — to hell with the APA.

True; depends on the style guide, but most opt in that direction. The Chicago Manual of Style is very firmly in favor of it.

It's more a matter of continent than style (ie, the former can explain most of the variance).

The alternative is usually en-dash with spaces.