and immediately tells me that the person making the wager is not too bright when it comes to gambling. It seems completely illogical to bet the SAME amount on a horse to W/P/S. A show wager in itself is normally a poor decision, except on big racing days like Breeder's Cup and the Derby where the fields are solidly matched and you can hit a big payoff for third.
And back to my original disdain regarding "Across the Board (ATB)" betting. Let's say you were going to bet $10 ATB for a $30 wager. I think you would be much better to just bet $5W/$10P/$15S so you still probably make a little money or lose little if your horse comes in third. Even better, in most races, eschew the show bet all together and instead bet $10W/$20P.
At Derby parties, even the cheapest bettors will bet $2 ATB instead of the much better $2W/$4P or even $6W instead. The bigger money should always be weighted down on the place and show bets if you are going to bet W/P/S. The ATB bets quickly add up when people are consistently doing this with 7/5 chalk, and it is low reward even if the horse finally wins.