Free Software's Fifth Freedom

I wouldn't call this a "freedom". More like an option.

In general, open source projects with a vibrant community provide a lot of benefits including:

1) Developers who already know the API and possibly inner workings of the tool before you hire them

2) Constant improvements, bug fixes and security patches for free

3) Standard base on which to build projects, making it easier to hire someone or join a team

4) Greater chance someone ran across your particular issue

5) Less lock-in

etc etc.