They were popular with hunters way way back in the day and I HEAR they're getting to be popular again in the A circuit (particularly in the derby field). They're supposed to accentuate a nice bottom. :) And if I remember correctly there are a few patterns that are "traditional"- checkers, triangles, and maybe stripes? And I THINK the different patterns were used for particular horses. Like the triangles were for green horses? Checkers were for geldings or something? I don't remember the details! But there are some really cool designs out there these days!