Sandbox refresh is a great way to ensure the metadata between your sandbox and production are aligned. Depending on the type of orgs you use, a refresh may also include some data seeding too. However, there are restrictions on how often a sandbox can be refreshed, so sandbox seeding is the best way to keep your sandbox populated with realistic test data between refreshes.
For sandboxes that aren't populated with data during the refresh process, sandbox seeding is a quick and easy way to get test data into these environments.