Even if one doesn't need to actually change them at any time, being able to set them at runtime through inlets is absolutely necessary if one wants them to be computed as a function of some of the containing patch's creation arguments.
At least untill we will be able to write expressions in creation arguments that would be evaluated at creation time. (but even then, we won't be able to write _programs_ in creation arguments!)
Imagine for example you want to make an abstraction that computes the amplitude of the signal and takes an approximate RATE (analysis per second) as creation argument. You just can't.