It is very helpful that you can send messages to your coachees through Slack or any other communication platform as well! I like this so much, because at times it takes time for an email response from my coach.
Also, sometimes they are slow when replying me back with answers regarding questions raised by them during our interaction sessions via calls/Skype meetings etc. However, overall we find great benefits out side using VAC services than just going over chat while doing virtual training session. We have been solving many issues related to hiring process management which has helped us immensely.