What drives me nuts is that there are so many of these things.
I know groups that (for business or pleasure) use Slack, Discord, Skype, Google Hangouts, IRC, etc.
All of these clients are a bit more obstrusive than they need to be in terms of pop-up notifications, software updates, cpu, memory, transfer, etc. They all screw up enough that there's always a little apprehension that something will go wrong when you get a number of people together for a meeting.
It is one thing to deal with one of these things, but when you have to install ten to get your work done you have a problem. I have a high performance computer and I want to keep it that way.