In my experience, locked grooves became more interesting (and useful?) when used with a decent outboard FX unit - and filter, or when a 3rd deck is utilized. The 3rd deck treatment hasn't happened very often, but with an FX unit and filter I found that the loops could be modified and twisted far beyond what the original form was. This allowed you to create your own transitions, interludes, or even a completely different melody or rhythm. Used with some imagination they can be a very useful tool.