I have found it depends particularly on what you will be doing at the bench. For woodworking, it's recommended that you drop your arms by your side, put your hand flat (fingers facing forward) and measure from the palm of your hand to the floor. The thinking here is that when you're doing handwork (ie. plane work, handsaw, chisel, etc...) you'll get a bit better leverage when the work is a bit lower. That being said, if I were tying flies for fishing or something, I'd definitely want something taller.