Too much series resistance in loudspeaker wiring pops up from time to time. Sometimes long runs are unavoidable, so the question of what wire size must be answered. But aside from the rather obvious loss of sensitivity, meaning increased line loss, what else happens?
Conventional loudspeakers have extremely low impedance, perhaps four to eight ohms, and if a similar resistance exists in the wiring then the sensitivity drops 6 dB. One might look at powered units but frequently power is not available at the location of the loudspeaker. Using 70 V lines and transformers is another choice.