Is a Controller needed for systems without generators?
HOMER requires a Controller even if the model doesn't have a generator, but according to the documentation all dispatch strategies control how the generator(s) interact with the battery bank. It doesn't seem like a Controller should be required in a model without any generators and that this Required Changes warning should be relaxed.
The controller in HOMER Pro is not just specific to generators serving loads or charging battery banks. It calculates how all available sources of energy are committed to serve the load and charge battery banks. So the source need not necessarily be just a generator but can also be other sources like PV and wind. Hope this answers your question.
The difference between LF and CC can be realized only with dispatchable energy sources which are generally generators but this doesn't mean you don't need a controller for other sources. The controller can be considered analogous to the ALU in a computer processor to explain in simple terms. The strategies may or may not be different for different models but is essential to perform any energy calculations.