It would be quite convenient for some workouts, such as indoor rowing imported from Concept2 logbook via TCX files. They are recorded with no splits at all in Garmin Connect, although some other applications / websites provide at least a standard distance lap breakdown (500 m for rowing, 1 km or 1 mile for running, etc.).
Adding a simple editing tool to break workouts by manual splits by distance or time would make a huge impact, people would be able to analyze and contrast imported interval workouts and any workouts with uneven non-time based intervals such as bursts and pyramids for rowing.
