I know what you are thinking: You think I am the type of person that does not set tasks, objectives, or goals and then shatters them. On the contrary! I have been using Slack for about a month and a half now, and I can honestly say that it has improved team communication, 10-fold (in my short-term personal experience)!
It starts with one Email (Generic Scenario)
Picture this for a second: You create an initial email that you plan to send to your development, marketing, finance, or whatever team you are a part of. You get a response from your colleague(s). Your team creates a chain of responses. This results in hundreds of email threads, mind you. To complicate things, you might also send a file or two back and forth. Or even a hyperlink that leads to a .zip folder containing the financial projections for the next 2-3 fiscal quarters. If revisions have been made to any document, folder, etc.: expect your email threads to be in the thousands at this point. This email conversation has been days, weeks, months in the making. This is all well and good, until…
The Aftermath
Now, it is time to have one if not several copies of those projections in your hand. The meeting in which you present these at, commences in 20 minutes. Since email was used, it is now time to go through your emails and find that conversation. You first let some expletives fly followed by sweat (profusely). Once found, you have a sense of relief for a moment until you realize that you now need to go through each & every thread with a fine-tooth comb in order to find the exact email that holds those documents (the golden ticket). You stop sweating and start having a heart attack. If you are lucky and you find those documents immediately, you feel like a Super Bowl Champion because you have just saved yourself a monumental amount of time in which otherwise would have been wasted on scavenger hunting. You feel fervidly relieved.
Here is what my email looked like before Slack:

Here is what my email looks like currently (theoretically speaking):

The reason why I say theoretically is because as a college student, here are the emails that I receive, regardless:
- University Newsletters
- Messages from the University President
- IT emails regarding server maintenance or system shut downs & reboots
- Professors posting new assignments, grades, or documentation from lectures
- Other student organizations that are advertising their upcoming events
I receive those emails whether I want them or not, they are out of my jurisdiction of control. But what I can control is the communication between my organizational Board Members, colleagues on group projects, etc.

If I need to communicate with my teams about something, Channels are used to talk about certain topics or to certain teams – only those involved in those channels will be notified and can collaborate with me. Do I want to make a general organizational announcement, event announcement, or scheduled meeting announcement to my entire team? I jump into the ‘general’ channel. Do I want to discuss and collaborate on the financial projections for the next 2-3 fiscal quarters? I jump into the ‘finances’ channel. Do I want to discuss a private matter to only my Executive Board? I jump into the ‘executives’ channel, and so on.