Two different scopes. If you utilize the ADO transaction everything called with that scope will be in the transaction. But if you handle the transaction within the SP you can limit it to only the portion of the SP you want to be in the transaction. Sometimes the ADO transaction would be good and other times the limited scope of the transaction in the SP is better.
All my SPs will have transaction handling as needed within the SP but will respect transactions outside of the SP as well.
Sr Database Engineer