Ironically, I personally prefer good typography, but unless the editor for the desktop app is autocorrecting -- to —, I usually don't bother. But when I type on the phone with screen keyboard, I almost always do bother, even though entering text on mobile is objectively slower and more difficult and often with fewer options.
>>Andrew+(OP)
In this particular case, the options for mobile 'phone keyboards are greater rather than fewer. The em dash is a first class citizen on the "writer" layouts in ThumbKey, for example.