Verification can be useful where there is a need to cross-reference data against a primary source. For example the project might be cataloguing data about a physical asset such as a book or a business. Or a lot of data may have been imported as a Bulk Change.
Submitting Evidence is a way for contributors to indicate the provenance of data, whereas Marking as Verified can help to indicate that other contributors have checked that the sources or observations are correct.
Marking a record as verified could be considered one of the smallest useful contributions to the database. You could signpost contributors to these tasks as part of their Learning Curve.