Use for the flow start point.
The Begin flow event type marks up the profiler sample as a flow start point. The new flow identifier is generated for the Begin event.
Use it to track all profiler samples which belong to the same flow. Next denotes the next point of the flow and End denotes the flow termination.
Flow identifier starts from 1 and is incremented by 1 for each new Begin.
Example of the flow start point is a job scheduling. IJobExtensions.Schedule generates an implicit Begin profiler flow event and IJob.Execute Next event.