Providing you with a snapshot of your current vulnerabilities. Performed monthly, weekly, or constantly.
A vulnerability assessment or penetration test will provide you with a snapshot of the vulnerabilities you are exposed to at the time the test was undertaken. If a new vulnerability is released or your equipment is misconfigured after the test, you will be exposed until your next test is performed. If your tests are only scheduled annually, this window of exposure could be extensive.
Continuous vulnerability assessments are performed weekly or monthly and will greatly reduce this exposure.
The scans are most external though internal scans can also be provided in the same way.