I think the other side of this is that some folks tend toward perfectionism in their writing, so in an atmosphere where writing standards are perceived as very high, people can spend way too much time and energy trying to put things in just the right way, when they otherwise could have gotten their ideas across in a few seconds using a "stream-of-consciousness" style that is more similar to casual conversation. It ca…
People should go for the middle ground on Slack. If you miss a period, so what? But skipping all of them just to be "casual"? That induces a cognitive load on your reader that you shouldn't.