I haven't worked for very large organizations and I've never worked for a company that had a "Build Server".
What is their purpose?
Why aren't the developers building the project on their local machines, or are they?
Are some projects so large that more powerful machines are needed to build it in a reasonable amount of time?
The only place I see a Build Server being useful is for continuous integration with the build server constantly building what is committed to the repository. Is it I have just not worked on projects large enough?
Someone, please enlighten me: What is the purpose of a build server?
The reason given is actually a huge benefit. Builds that go to QA should only ever come from a system that builds only from the repository. This way build packages are reproducible and traceable. Developers manually building code for anything except their own testing is dangerous. Too much risk of stuff not getting checked in, being out of date with other people's changes, etc. etc.