Liner panels serve two purposes. They enhance appearance, giving the interior a more finished look. Just as importantly, liners protect the insulation and the outside walls. Unreinforced insulation facings tear easily, and even the best reinforced materials can be damaged by sharp objects or power tools. Although 26-gauge exterior walls can withstand a lot of punishment, forklifts and other heavy equipment can dent or even puncture them. A steel liner that has been designed for your metal building
will perform far better than plywood and usually cost much less than sheetrock walls, which will require their own framing.