This is group culture dependent. For us, people popped in and out as needed. We cheered when someone said "I need a slack break" and signed out for a day, and were glad when we saw people clean up their channels because we knew they'd be able to get more actual work done. We got there because people just decided to purge one day, despite maybe looking bad. This normalized the behavior over time. It's just like walking out of a meeting saying "y'all got this, I'm not going to be of help". It can seem rude to some, but it can also seem rude to stick around just to for looks.