A single scan tells you what was there at one moment. The day after, a new subdomain might go live, a service might change, or something might disappear. If you only run scans quarterly or annually, you're blind to change for most of the year.
Baseline + refresh
The answer is a baseline snapshot—an authoritative view of your surface at a point in time—plus regular refresh runs. Each refresh is compared to the baseline so you see exactly what's new, changed, or gone. That's drift detection. It turns "we scanned once" into "we know what changed and when."
Continuous assurance
For regulators and insurers, continuous assurance means you can show a timeline of monitoring and response. Drift events and refresh cadence (e.g. daily) prove you didn't set and forget. That narrative is what they're looking for when assessing due care.
Summary
Drift detection isn't a nice-to-have—it's how you turn EASM into a defensible, continuous programme instead of a point-in-time snapshot that goes stale.