A full system snapshot is not 100% always the correct solution, data protection is complicated.
An example hypothetical, you have deeply embedded malware and you're unsure when it infected the system, it could have been sitting latent for months. In this situation you have to restore back and lose months of application data or restore a recent snapshot and then try to remove the malware in a clean room. It is much safer and easier to start from a clean OS and then restoring only the data on the system which is much simpler to scan for infection and sanitize.
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A full system snapshot is not 100% always the correct solution, data protection is complicated.
An example hypothetical, you have deeply embedded malware and you're unsure when it infected the system, it could have been sitting latent for months. In this situation you have to restore back and lose months of application data or restore a recent snapshot and then try to remove the malware in a clean room. It is much safer and easier to start from a clean OS and then restoring only the data on the system which is much simpler to scan for infection and sanitize.