Just because you can do something currently, doesn't mean you will always be able to do it. Take sight-reading, for example.
When I was growing up, and until I got into the orchestra, I was an excellent sight-reader. That's what I was told by others and I knew myself that I was pretty good at it. This ability stayed with me through my Empire Brass days--all of those guys were GREAT sight-readers.
After I left the group, the need for me to sight-read difficult music occurred much more infrequently. Occasionally, we would get a Boston Pops piece in the morning and have to play it on a TV show that evening. The same with Pops recording sessions. A piece would turn up in the handwritten manuscript of the composer (oftentimes, divisi) and then the recording light would go on! Time for the first run through! But there was no demand for me to sight-read on a regular basis. Since I knew what the orchestra would be playing a year or more in advance, I started to see my sight-reading get rusty.
Then I noticed a lot of students sight-reading was not very good. So, I decided to write a sight reading book using four clefs (treble, alto, tenor and bass). I titled the book "Reading at the Speed of Sight."
The book is not easy at all and was designed in such a way that most of the studies are not predictable in their harmonic outline. In other words, they are not meant to be beautiful nor meaningful in their musical content. The purpose is to develop sight reading-skills or to improve the sight-reading ability we have--or used to have!
Many musicians who are freelance artists need to be able to sight-read. Many times they are called to play at a moment's notice and having good sight-reading skiills is valuable and impresses the employer and fellow musicians.
Sight-reading, in my experience, used to play a bigger role in orchestra auditions than it does nowadays. But don't use that as an excuse not to work on it. In additon to the reasons already mentioned, it's good for your brain! :-)
In the book, I include several different methods of approach which have proven to be very effective. Also included in the book are 20 sight-reading duets. They were inspired by Bartok's violin duets, in a certain kind of way, because, in sight-reading, assumption can be the mother of all screw ups! :-)
I think "Reading at the Speed of Sight" is an excellent book for advanced players--students or professionals who want to keep and build upon this very useful skill. It is available on the Studies area of our website, along with other texts and exercises. By the way, you can download (in pdf format) the first two etudes for free! Those are the easy ones--though not as easy as they look! ;-)