Slack, valued at $5 billion, has received buyout pitches from several companies including Amazon and Microsoft. But the team collaborations service, which has over 5 million active users, continues to offer one of the most resource intensive apps you could find on Mac and iOS. From an article: TLDR; If you care about battery life or availability of your finite CPU and memory on your computer, then you probably won't want to use Slack desktop with more than one or two accounts. Slack resource usage increases linearly as you add more accounts, and it quickly adds up. [...] I noticed that my machine has been sluggish and its battery life has become poor. Whilst investigating this, it turns out that Slack desktop fails badly when used with multiple accounts. This is because CPU and memory usage increases linearly as you add more accounts to your Slack desktop client. As a result, I believe the growing trend to use Slack to be part of multiple communities is seriously flawed until Slack resolve this problem.
The author, Matthew O'Riordan, has shared screenshots of Activity Monitor which shows that Slack application on his Mac was consuming more than 1.5GB of memory, and as much as 70 percent of the energy. The company's iOS app instills several more issues.