Every writer needs a filing system. Between research, queries, samples, and archives, it helps to have a system to keep track of everything.
And just as important as keeping track of the things you've written is keeping track of the things you are writing. That's why every writer should also have a system to keep track of active projects. Not only will it help you to know what you're working on and what you need to work on, but it will help you to keep your clients updated on your progress.