Why is documentation is necessary for software package?

Answer 1

Software documentation is not needed if the code and concept is perfect -- but that'll never happen. Seriously, documentation is needed for debuggging problems, modifications as times/requirements change, to figure out how hackers/crackers exploit loop-holes (and what those loop-holes are) and and and.... Does that help?

Answer 2

Computer documentation helps us understand what tasks a piece of computer software which we have purchased or are contemplating purchasing is designed to perform. It lets us know what functionality we can expect from the software and should give us fairly-explicit instructions as to how to actually use/configure the software. If after purchasing a piece of software we have trouble determining how to successfully accomplish something with the software that its documentation claims as a feature, the claims stated in the documentation become the leverage with which we demand technical support and/or engineering assistance/remedy from the manufacturer.