While we all wish to conserve our environment, we advise you to print out major changes to your manuscripts (assuming you are using a computer). Printing back to back is fine. Keeping all your manuscripts in electronic form may create problems in the future. Will the software exist to read them? Will researchers wish to read them online? The best solution is still the old-fashioned paper copy. Tying large manuscripts together using cotton tape protects and keeps them together. Remember to keep your research notes and journals too.