The Japanese preference for horizontal rod holders is prevalent in the majority of holders on the market today. Personally I also prefer using horizontal ones to vertical types, especially when bottom fishing, the line is away from the boat and bites can be easily detected during the quieter times when I'm not holding the rod. Generally Japanese anglers tend to leave their rods in holders much longer though, mainly because of the widespread use of electric reels.

From Daiichi Seiko