Having the ability to track a Lead without entering it as a Deal into your Pipeline is a great feature. There are many times we want to identify potential opportunities before they are truly qualified. If we put them in the Pipeline and they end up fizzling out, then it scues our win / loss ratio and metrics for tracking deal turnaround.
Now that this feature is available, it would be nice to have the option to convert existing Deals into Leads in order to maintain any historical activities that would be lost by deleting the deal and re-creating it as a lead. Please consider this for future updates.