I don't have a problem with that as long as it is respected when you are outside of work time (sadly in some companies won't be) - I'm in 4-5 work groups and just have notifications on silent, etc. and dip in and out if I have a spare moment, etc. occasionally it is used to request cover but aside from that no expectation of a reply. Personally I prefer it as it keeps people on the same page and communicating in a way that tends to breakdown normally in too many businesses.