With large projects working on each others code is essential. Programmers cant just drop their current project to fix a few minor thinkos in their code that are causing someone else problems. Programmers leave (and then become the instant cause of every bug and failure in the system :-) programmers drop projects, etc. While sometimes it rankles when it happens to your own code because you would have fixed it differently/better the fact is its almost inevitable with large code bases.

A good example is PM. The code base here has had many authors, we cant stand around waiting for those authors to show up to fix bugs or extend the code. If they are here and can do the work needed then fine, otherwise the work must get done.