What is the difference between Workflow trigger points ??

I am new to workflow . I need to trigger a workflow (Approval Reject) workflow on the creation of Sales Order . I used the T-code SWETPYV to create the event linkage and trigger the workflow .

In SWEL logs it is showing the workflow is getting triggered .

Now in SWDD transaction there is also a place where you can define a workflow should be triggered when the Sales Order is created .

What is difference between these two .ways of defining the trigger point . ???