Starting a remote agent with an actual user account rather than the system account, which is the default, makes a big difference for browser-driven virtual users. Each virtual user employs its own Internet Explorer instance, which loads the settings stored in the Microsoft Windows user's profile.
Under the system account, Internet Explorer loads different settings than under a user account. Typically Internet Explorer utilizes fewer or different HTTP headers than with user accounts. In order to avoid the issue of recorded traffic differing from generated traffic, it is recommended to run remote agents under a user account.
The required account setting can be configured in System Configuration Manager on the Applications tab or a user account can be set in the tab if all remote agents should run under the same user account.