"mostly smooth" is sanded almost all the way smooth, very little variation in height between boards, equal quality, more likely to come from the inside of boards or beams rather than the outside textured face, will have less character, still looks reclaimed, will have nail holes to stain but no weathering or deep saw marks, easier to clean, easier to fully sand and refinish, more affordable. "skip sanded" always come from the outside dirty face of boards, some circle sawn or weathering remains, slightly more variation in height between pieces of flooring (could have height difference of up to a 1/16”), more rustic, takes longer and is more expensive to manufacture, most people want this textured look.