For me it's their speed, yes. I only run 0-3 at a time, and often the problem at hand is very much not complex. For example "Take this component out of the file into its own file, including its styles." The agent may take 5 minutes for that and what do I do in the meantime? I can start another agent for the next task at hand.

Could also be a bug hunt "Sometimes we get an error message about XYZ, please investigate how that might happen." or "Please move setting XY from localstorage to cookies".