Why are you compiling? I use synaptic package manager (system -> install/remove software) to install gcc and g++.
Sheng-Chieh
You can program something yourself for instance. And compile.
And sometimes you want something which is only in 'source-code'.
I know a distro where the packers demand source when you make a request for some program in the repository.
That's an important factor of Open Software. The source is always available if you insist.