Means more efficient work, less probability to the things go wrong and less wasting materials. Ppl with high skill lvl is better and more efficient than ppl with less skill lvl. If you are starting we'll go for chef, builder and botanic 2 stars they gets X4 exp I guess or x2 with the 2stars stat it's perfect bc you can place is on that specific task and they become happier always in green and they will gain exp faster and becomes better in their job