Quite a few years ago, I invested in a Circa punch from Levenger. Even though Levenger sells a full range of Circa notebooks, etc., the American sizes (letter and junior) used are different from what we use here in Malaysia (the "A" system. including A4 and A5 that I use the most).
Altho the punch is very expensive, I'm glad I bought one as it allows me to make my own Circa notebooks (I also bought the Circa rings at the same time) from recycled A4 sheets (printed on one side, blank on the other).
The Circa punch makes "open" holes on the paper so that, instead of opening up a binder to take out pages to rearrange, you just pull the pages off the rings without needing to open a binder. This way, I can write up notes in one section of the notebook and later pull them out to rearrange in their respective sections of the notebook.
Tammy Cravit is another Circa fan and explains its use better than I do:
Of Notebooks and Writers' Tools