I've talked about the importance of paperwork and admin tasks many times. There are also guidelines and rules about how long to keep things. Much like financial advisors tell you to keep tax returns for 7 years, you should keep your paperwork as well.
While these are not legal guidelines (I am not a lawyer), these are good faith practices that you should follow. I do recommend talking with your HR rep to determine what guidelines your specific company may have.
Keep all performance related notes and paperwork for at least 1 year. This helps you because when it comes time for any formal performance reviews, you will have everything you need at your disposal to do research and write things.
Keep any contracts or agreements for at least 2 years past their expiration date. It always helps to have a copy on hand in case issues arise and/or you want to use it as a frame of reference.
Performance reviews. Keep them for as long as the employee works for you. If someone else takes over your department, give them the files. They may never look at them, but if they need something, they will be happy it is there.
Emails. Delete as soon as possible. One of the biggest inefficiencies I see with managers (and all employees) is there mailbox is too full. They miss things and can't find things. The only exception to this is if you have been told of a potential or actual lawsuit where emails may be requested as part of discovery. If that is the case, talk with your IT and Legal department for the best way to archive the files to ensure compliance with the law.
What other guidelines do you or your company have regarding paperwork retention?