I couldn't imagine writing without at least attempting to use proper grammar. Especially in German where ignoring capitalization makes a difference of night and day.
My reasoning has been similar to the one of the author, but more on a "positivity" than a plain productivity level. If it's easy for others to read my messages and not having to puzzle over them, I hope that it will leave them with overall a more positive association of writing/communicating with me. And that not only goes for professional texting, but writing with friends (or dating) as well. I know it won't always come out perfect, but overall I think it shows some level of respect towards the other person.