Every question you answer on the mailing list will save someone time and, if done well, will actually improve your own knowledge. The project's developers will often answer technical questions that require substantial understanding of the code or suggest a possible bug. Setup issues, though — connecting and logging in to the server, getting Apache going — are questions many experienced users can and do answer, thereby fostering the community on which the project depends.

Your experience may well be more closely aligned with the question posed than that of anyone else reading the list that day. You may use that framework or language or OS, or have that particular server. No one, no matter how expert in the code, has used every configuration, version, OS, compiler, etc. Whether you simply confirm there's a problem in some particular arrangement, or say, “dunno, works for me”, you're adding information.