The list is endless...
The older they get the better value for money if you manipulate the situation wisely.. Look it like an investment for the future, You need to stay ahead of the game though, in their early years they are easily manipulated then as they get older they get wise to your schemes and tricks so you have to keep coming up with new ideas to cover the same ground.. There will come a point though where they cannot be controlled at all and they go feral and get out of control.. however, with a careful well placed long term strategy they will soon come back under your wing... The last part is a gamble though because they can flee the nest at some random time leaving your long term masterplan in tatters..
This is why I had 4 so I could have a fall back plan in the event of disaster...