I do the same, and it makes training the next generation so much easier. Your just-created assassin has between a 1-3 in Subterfuge. If you've managed to collect a pet monkey, catamite, and courtesan all on an older assassin, transferring them to a young rookie will turn a 1 into a 6 right off, giving him a much better chance of killing those low rank targets. It doesn't take much at that stage to gain a couple more points of skill.