do you have a specific case?
There are so many different cases, its difficult to give a general advice without more information.
Well, a trivial case would be controlling an alpha value in multiple shaders. That can be handled via reference shader, but the Carrara interface tries to prevent that by not allowing specifying a reference shader at the level. Cut and paste works, but the shader does not preview correctly. OTOH using ERC sets the value directly and the preview is correct.
Now, if you base the alpha channel on fake fresnel it gets more complicated. For example, one set of domains might use fake fresnel with a roll off of 33.33% and others at 50%. By mixing that with another setting (say Minimum with a value) there might be three controls: two for roll off and one for minimum. This can be satisfied by using two different reference shaders, but as noted the Carrara interface works against you and the more interrelated values shared between shaders and the more shaders involved the more awkward it is to use reference shaders. ERC provides an easier way to accomplish this—except for the apparent inability to have one slider control settings in multiple shaders.
That is more or less what I’m trying to do at present but managing shaders in general profits from this. For example, to have a slider that drives two values in a single shader, such as multiplying a color and an alpha value. Again, technically reference shaders can be used for this but the interface works against you—and most effects can be achieved multiple ways, eats a matter of ease and facility. Tim Paynes work with only the basic Carrara shaders is amazing, but it is easier to do things by using various add on, such as Fenric’s and Digital Carvers Guild.
I hope that clarifies things a bit.