The BizTalk Server host throttling mechanism continually monitors for a throttling condition, calculates the severity of the throttling condition, and applies host throttling progressively depending on the calculated severity. The throttling mechanism is self tuning and the default configuration options are suitable for the majority of BizTalk Server processing scenarios. BizTalk Server host throttling exposes several configurable options that can be used to tune throttling for specific scenarios. For information about changing these configuration options, see How to Modify the Default Host Throttling Settings.

source - msdn