I strongly believe answers on AU should be self-contained, complete and independendly usable. External links can be useful to add interesting stuff, to link to a more advanced version of the script or a possible ppa, but the answer should still work without.
Scripts, why not (only) post elsewhere?
###Scripts, why not (only) post elsewhere? IfIf you post an answer to my question with a script, I want to look into the code, make an educated guess on the quality, see where it has downsides etc. Even more inportantly, I want other users to look into the code and see possible issues, be able to comment on it and suggest improvements. The joined knowledge is one of the most important fundaments of the site. Improvements are suggested to all answers here, including scripts.
This process is unlikely to happen if the code is not directly visible and readable in the answer itself.
Difference with existing software
###Difference with existing software TheThe comparison with established software is invalid. Not only is established software less likely to have major issues, but if there are, more users will have run into the same issue(s), and can share their experiences. At the same time, posted scripts are by definition in an experimental stage.
Last but not least: the more parties are needed to make the complete answer available, the more likely it will sooner or later break; the weakest shackle defines the reliability of the entire answer being available.