It shows how much/little care the author has about their own subject and the reader. Just like people that don't use punctuation.

If they're not willing to make it readable, I don't care what their message is. All I read is "I'm a lazy fuck! 😀" 

 listenhereyouwhinylittlemotherfuckensunnuvabitchiwilltypehoweveriwanttotypeandyoucandonothingaboutitexceptcomplainmmkyougotthatnowfuckoff