As Roland said, people have specific roles. Programmers are not interchangeable. Over time two can be if they both learn a system well, but that rarely happens, since there is plenty of work to spread around. New programmers can be a time drain, since they often have to ask other programmers how stuff works and sometimes you could of just spent that time fixing it yourself. Then you get new bugs while fixing bugs, which just happened recently when a consultant tried to fix a bug where they don't understand all the game features, then I spend time looking at their bugs and trying to help, blah, blah, blah.