It's really convenient. First of all, it's useful for communication within a certain company. I first faced with Slack with the beginning of the lockdown, when we worked remotely. We communicated with our co-workers within slack. It allows to create groups and categories, set reminders, etc. Then we also adjusted messaging via slack sms with our customers. It somehow reminds well-known social messengers like (Telegram or Messanger), but I'd say it's more structured.