vSphere snapshots are useful in quick rollback scenarios where you might have issues with OS patches or changes to an application. They should not be kept long-term because they do increase in size over time and can impact the performance of your VM.
See https://communities.vmware.com/thread/249830
We have a 5 day rule where we delete all vCenter/vSphere snapshots after 5 days. I created a WFA workflow for it and will post it soon if anyone is interested.
VSC snapshots are better for slightly longer term storage but I believe they are still techinically snapshots and not a viable option for long-term backups.