Hello , let me explain with an example. If there are four request in psa and our target is DSO.
first lets run the delta DTP , it will load all four request to DSO provided load request by request is selected , now if you run the delta again it will not update any request as all the requests have been updated.
Now lets run the full dtp , it will always load all the data from source and consolidate into one request. again if you run full dtp it will fetch all data but in case of delta once request has been loaded to target the staus gets updated in source that this request has been loaded.
Hope this is helpful.
Thansk, Saveen.