Look at the Tsiolkovsky rocket equation - a rocket's delta-v (velocity change potential) is proportional to the log of its mass ratio (its mass with fuel divided by its mass without fuel). For modern rockets, that means about twenty kilos of fuel for every kilo of anything else (the rocket included). You really don't want to add structural mass if there's any way to avoid it.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.