Scenario: You just received the collection of papers from great aunt Gertrude. How do you decide what to keep and what to get rid of?
Your first thought may be “Aaaack! I don't have room for more boxes. Maybe I should do a fast sort and dump.” However, I would advise against this. Here's the most important reason why: some of the things that seem unimportant or mundane now may later provide clues to tracing someone or understanding their life better.
A concrete example might be finding an obituary for someone whose name you don't recognize. Perhaps it was just a friend, but in a few years when you have done more research you might recognize it as someone who married into the family. A closer look may reveal a new married name for one of your people or a city of residence that you were unaware of. Either way, that little clue may be just what you need to track someone down, just like sometimes it only takes one additional letter in a crossword puzzle to allow you to fill in an entire corner.
I'm sure we've all come across notes we took when we were just starting our genealogical adventure. It is always rewarding to see that we've made progress over the years. We now have a history for the sister who had seemingly dropped off the face of the earth. We now have land records and newspaper articles to teach us about people we only had the barest vital records for before.
My mother and I keep encountering this phenomenon. When she comes to visit she brings a bag or envelope with family stuff enclosed. Some of the items I've gone through before, but each time something there has new meaning because I have learned more. In the most recent batch I went through notebooks my grandmother kept when she and my grandfather were building their house during WWII. They built on a lot where the previous house had burned. My mother told me my grandfather salvaged everything he could, nails, bricks, you name it. He measured every board he saved and then used that information to determine how much house he could build. My grandmother's notebooks list how much everything cost, down to the price for a box of nails. On the surface, it may not seem interesting, but when put in the context of the war and knowing this was my mother's childhood home, I'm glad we saved these notebooks.
I now try to put notes with each collection of items as I sort through them. The notes may be brief descriptions of the contents and notations of what I scanned. What I now realize needs to be added is the date I examined them. This way I will know how long it has been since I perused the documents and therefore, how likely it is that I will find something I didn't know was important way back when. As much as I want to decrease the clutter in my life, I don't want to be too hasty in my efforts and discard something I might regret later. My advice would be to keep it (for now) if you are in doubt. You can always change your mind later and toss it, but you will never be able to retrieve something that went to the landfill or the recycling center months or years ago.