Selenium test scripts are used by QA teams to reliably test functionality in a repeatable manner so that working features don't break as new code is introduced in an application. InsightAppSec and AppSpider are able to leverage Selenium test scripts to optimize coverage of a target application, by providing coverage where a crawler can't or by covering key areas that are of particular interest such as the pages of a new feature. With this integration, critical areas of an application aren't left untested.
Most enterprise testing teams already use test automation tools & scripts such as Selenium to create repeatable tests that can be executed in conjunction with nightly application builds. It only makes sense to integrate security tests into this as well so that security tests can run automatically every time the application changes. This is a great way to catch web application security vulnerabilities early in the SDLC.