The question is where the work already happens
A web application asks people to leave what they are doing and go somewhere else. An extension meets them inside the tab they are already working in. Neither is better in general; the right choice follows the workflow.
When staff copy data out of a supplier portal, a CRM, or a client website into a spreadsheet, the copying is the problem. That is extension territory.
Choose an extension when
The value comes from context that only the open page has.
- The workflow starts on someone else’s website
- Data must be captured from pages you do not control
- Users need a shortcut without breaking their current task
- Evidence, screenshots, or page state matter
- The alternative is manual copy-paste between systems
Choose a web application when
The value comes from what happens after capture.
- Multiple roles need shared visibility and approvals
- Reporting, history, and audit trails are the deliverable
- Clients or contractors outside the team must participate
- Billing, permissions, or tenant boundaries are required
In practice most teams need both
The strongest pattern is a thin extension for capture and action, with a web platform that owns identity, permissions, history, and reporting. One account model, one API, one place the data lives.
Building them separately usually means paying twice: once for two auth systems, once again to reconcile the data. Scoping them as one system from the start avoids that.