Sounds good in theory, rarely works well in practice.
The only times I've seen Slack work well is when everyone involved starts with similar expectations about how it should be used and what's appropriate. In my experience, this is easiest to achieve when Slack channels are closely aligned with teams who are working together.
The model tends to break down when Slack is used for communication that is better served by e-mail, calls, or meetings. An easy rule of thumb is that if it crosses department boundaries and/or is something that needs to be formally communicated to an entire team, it's better to direct it to e-mail or a scheduled call.
> Speaking of the example in the article, there is absolutely no reason clients should have direct message channels with your company's employees and expect to get a response 24/7.
Strongly agree, but it's not just clients. Sales people, for example, love to use Slack because it's a backdoor channel to circumvent management and go straight to the engineers.