All I've ever heard about only BD every two days or longer is because the sperm COUNT goes down - the guy's body can only replenish itself so quickly, and has a maximum limit that it will reach after a few day's recharge (usually 4 days from what I've read). BUT, that's only the number of sperm. Only ONE is needed, and the count is usually in the millions. So what if it goes from 10 million to 7 million? Timing is a HUGE deal, and if you have enough sperm that is mobile enough to travel the distance to fertalize the egg if timing is right, then... why not?