何时使用构建工具？

A beginner question, bear with me: I'm just wondering under what circumstances one should use a build tool like nant or msbuild? I'm working on a medium sized application (.net 3.0), every developer is doing his work and builds on his machine checking his code changes into the repository as he goes. Once we're all done, I'll get all the code from the repository, make a clean build on my machine and we deploy the binaries. Just out of curiosity, where comes the build tool in?A beginner question, bear with me: I'm just won