I've been using Slack for a few years now. I use it more for work than anything else. I am part of a number of different client teams and it's through these that we do most of the day to day communication. I have to be honest it has become something of a necessary evil to have, but it is an easy way to stay in contact with clients. For clients that have only a handful of employees then I recommend that we just stay in touch with phone calls, emails and of course whatever project management tool that works best for the client.
Benjamin Pollack's post about his issues with Slack are good points and with more people turning to apps like Slack, it's worth remembering that Slack isn't a great tool and should only be used if there is a genuine need for it other than, "Hey I need this right now!".
Perhaps the greatest argument against using Slack isn't the filtering of communications or the notifications.
It's the version of Markdown that Slack uses for it's messages. It's just not Markdown.
5. Its version of Markdown is just broken
I’m going to use up an entire heading purely to say that making *foo* be bold and _foo_ be italic is covered in Leviticus 64:128 and explicitly punishable by stoning until death.
— Why I Hate Slack and You Should Too by Benjamin Pollack
What grieves me more is that there isn't a week goes by where I don't end up sending a message formatted incorrectly because Slack has it's own version of Markdown.
Slack isn't a necessary evil but teams should consider Benjamin's points before deciding if Slack is worth using.
Give me email and a phone any day of the week.