I unconsciously mimic the other person's formatting when replying to emails. They double-space? I double space. They sign each message? I sign each message. etc. Same with instant messaging, e.g. whether someone says "lol" or "haha," or whether they use emotes or emoji.
My personal style is double-spaced paragraphs, emotes instead of emoji, Oxford comma, and (probably too many) semicolons, em dashes, ellipses, and parentheticals. Also, I rarely capitalize the first sentence, probably out of habit from instant messaging.