I'm sure a lot of people here on PianoStreet, especially more advanced members or those who have been playing for quite a while, have a lot of sheet music lying around. But how much of it have you actually played? You probably have at least a couple massive Dover books lying around with every Mozart sonata ever written, every Scriabin prelude, every Beethoven sonata, every Lyric Piece by Grieg...but would you even recognize half of it if you heard it? How many hidden beauties are lying in your ever-growing stack of sheet music that you have never gotten around to looking at?
Well, there's only one way to find out, isn't there?
Switch gears for a second:
Are your sightreading skills poor? You can play a Chopin etude but would struggle to sightread a Bach invention? Ever just want to play something for a group of friends but can't because goddammit, you're working on three extraordinarily difficult pieces at the moment and none of them are in quite good enough condition?
Well, there's only one way to fix that, isn't there?
...
I mainly made this post to encourage people to go through their music and try to sightread it all. Yes, it all. This will take forever. Depending on how much music you have, how often you sit down to sightread, and how frequently you buy more music, this could
literally take forever--your collection grows faster than you can sightread it. But it will be rewarding, both in how much fun it is, and how much your sightreading will improve, and best of all, you'll find beautiful music you would never have found otherwise.
I've been working on sightreading since this summer, although I did almost nothing during the term due to time constraints. But it is tons of fun, and you should all at least consider trying it. It's especially nice if you have a way to keep track of what you've gone through. It makes you feel like you're making progress somehow, at least for me, anyway.
To keep track of what music I've played, I made a spreadsheet. At the moment, it's quite barren, but it's getting more filled almost every day. Here's a sample of part of it...

As you can see, most recently I've been working on sightreading Scriabin's op. 11. I can honestly say that I love every single piece in that opus. And there's no way I would have found that out if I had only played no. 6, the one I've spent time working on.
I encourage you all to try it. And if anyone is interested, I can upload my spreadsheet as a model.
Lastly, "I have too much music, there's no way I could get through it all" is absolutely no excuse. It's not about getting through everything, it's about improving your sightreading ability and widening your horizons as to just how much music is out there beyond the standard pieces everyone plays. I've seen far too many people playing Fantaisie-impromptu. How many of you have ever played any of Chopin's other impromptus? How many of you have even
heard any of Chopin's other impromptus? That's what I thought. Even if you just play one new piece a day, your sightreading will improve and you will be exposed to more and more music.
So, basically, just play through music you've never played before. You'll become familiar with more music, you'll improve your sightreading, and by improving your sightreading, you'll be able to learn new music faster so you can widen your repertoire quicker. There are no downsides!