When designing startup files, you should keep the user in mind. If you are the only user on a machine, you don't have much to worry about ” if you make an error, you're the only one affected, and it's easy enough to fix. However, if your new startup files are to be the defaults for all new users on a machine or network, or if you think that someone might copy your files for use on a different machine, your task becomes considerably more difficult. If you make an error in a startup file for ten users, you might end up fixing this error ten times. That's annoying, to say the least.
There are two essential goals to keep in mind when creating startup files for other users:
Simplicity Keep the number of startup files small, and keep the files as small and simple as possible so that they are easy to modify but hard to break. Each item in a startup file is just one more thing that can break.
Readability Use many comments in the files, so that the users get a good picture of what each part of a file does.