Liners are normally worn under ulcer care compression stockings and alternative compression wraps. Some provide light compression. All of them protect the outer stocking from dirt, oils, and bodily fluids which will increase the life-span of the outer stocking.
A number of liners contain silver which is naturally anti-microbial and anti-fungal. This is especially important if you are treating a venous stasis ulcer. Keeping the wound free from bacteria will help it heal faster.