The "Only Once" Rule

A very organized friend once told me about her Only Once rule. When you receive a piece of mail, touch it only once and decide where it should go. It may go immediately in the trash (ask yourself if you will even truly need it again) or into a file. GTD seems to be somewhat similar to this. I pledge to try this process: collect, process, organize, review, & do. A problem with this is that there's such an array of tasks that we deal with each day, from creating a grocery list to work projects. I am curious, however, if this process can be applied to these various situations. This means that I will need to be somewhat ruthless by asking myself with each new email if I think I will ever need to deal with this again. In most cases, the answer will be no.