A fibrous bristle load holds significant amounts of water which mix with the soap lifted from a shaving mug or scuttle. The more water a brush holds, the moister and richer a lather will be. Thicker and more emollient lather translates to less razor skipping and dragging.
Bringing a shave brush across your skin produces a mild exfoliation. Because a shave brush is most often used with a shave soap, this effect often replaces the pre-shave routine of washing and applying lotion to the face.
The greatest benefit from shave brush use is the tendency to soften and lift facial hair before a shave. Applying shaving cream by hand mats hair or raises it unevenly. Shave brush use, however, requires agitation of the soap or cream in a mug to form a lather suitable for a shave, before application of the lather to the face in a gentle circular motion. Therefore, a razor does not need to be pressed to the skin in order to provide a close shave. For this reason, straight razors (or high-quality safety razors) are most often used with a shave brush, as it replaces the benefit of multiple blades