There could be some situations, such as T-8 to T-24 or something bigger, but it's not worth the difference when using any of the standard t-stuff (T-8,T-11,T-14,T-17, etc.). This is also because n 8wt. rod is generally very capable of handling a wide variety of payloads. Rather than carry two standard skagits close in grain weight, maybe you could consider an approach like this...
A 3D line (Airflo FIST, or something similar)
A typical floating skagit line.
I find the above to be very versatile, with a 3D line allowing you to more effectively fish certain types of waters and with lighter tips. A standard 24-30' head easily coils in your wading jacket and can be quickly exchanged. You can use the same running line for both heads.