I work at a data/dev consulting firm. We use Google Chat internally because its security guarantees are HIPAA compliant. We want that due to how often we are exposed to and need to share PII (for clients in healthcare).

However, many of our other clients use Slack internally and I use it to communicate with them... And I much prefer Slack. There's nothing really wrong with Google Chat, it just doesn't have the same polish or some of the really nice features that you might take for granted, like sane threading, custom emojis, or the ability to collapse a GIF so you can't see the animation out of the corner of your eye.