While Redash provides a fistful of features and available data sources/visualizations/dashboard layouts/alerts out of the box, it's not always enough to fulfill the needs of all of your users.
Data sources are very dynamic, and it won't be a mistake to note that you can definitely expect at least one/two totally new and not widely known data sources to become mainstream per year.
The same goes for alert destinations. For example, one day an email alert is enough, but as your company expands in new directions, you want Slack or Mattermost, or maybe Skype integration.
Your department manager is happy with the current dashboard layout and visualization type, but tomorrow you get a bigger screen to display your dashboards on, and all of a sudden you need a flower-shaped chart visualization.
If you use one of the closed source legacy dashboarding tools...