As a rule of thumb, your school filing system for paper should be no more complicated than the one you use at home, ideally less complicated.
Of course, if you like filing, feel free to make your life complicated: read about filing techiques here.
This comment applies to your personal filing system. Your department filing system and of course your school office system will be much more complicated. The intention is that you use these school systems for anything – letters from parents, last year's examination results – which you no longer need, but view as too important to throw away.
Incredible as it may seem sometimes, there are quiet spells in most teachers' school lives. These often occur when Year 11 go off to study for their GCSE exams, or maybe when Year 10 are on work experience, or when the boiler breaks and everyone gets sent home. It is very tempting to simply slump at this point, but I would encourage you to use any spare energy on this simple idea:
Trivia Day
If you have been following the principles embedded in the TM4T method, you will have been regularly prioritising tasks according to their importance, and deferring some things - even if you really want to do them !! Choose a day when there is one simple rule: you will not do ANYTHING which is important. You will just do those simple things on your to-do list that you want.
This is the point at which you go through your old filing and throw out things that you no longer need.