A server snapshot is useful to recover quickly. But a backup is quite separate :
Backups are generally separate from your server provider. If you lose access to AWS (maybe they think you are a bad actor or a billing failure makes them kill everything, this happened to me), then backups are a way for you to recover. Snapshots are almost always in the same server provider.
Backups are portable . You can't take a EBS snapshot and put it in Digitalocean
On Cloudron, backups are per app. So, you can restore each app individually unlike a server snapshot which will roll back everything.
Backups help in upgrading things. For example, you can upgrade/migrate database using backup of old version into new version.
So, they have different use cases. Both are useful. Use both when possible.