Apple's autosave and resume features are convenient for maintaining your workflow, even when you do not save documents. So in a program like Pages, for example, you could work on a document and simply quit the program or restart your computer, and the next time the program opens, your documents will be reopened with the changes to them preserved.
While convenient, especially in the event of a crash, hang, or power outage, this feature does have one potential drawback: it could reveal some personal or otherwise private information at inopportune times.
You can avoid this by quitting programs with the Option key held down, which will close all windows and not save the application's state, so when launched it will load its default views. This requires that you remember to do this before you quit. Additionally, this will immediately clear your current window arrangement.
An alternative approach is to launch programs but avoid restoring the saved state, which can be done simply by holding the Shift key when you open the program. By using this feature, you do not have to remember to close windows before quitting.