Well, I guess, it matters to me and when I see a student can manage, I feel obligated to make it happen. This is just my personality.
Several years ago, I talked to another teacher and he told me - why bother with learning so many pieces, why bring old pieces back, time is so short, just learn new pieces.
I can understand this point of view. However, I really feel that it is absolutely necessary to be able to bring "old pieces back", improve them. These are various skills that come in handy. Sometimes, it is necessary to be pressured to learn a piece in a very short time; it amazes me how able children are, nowadays. They do need to be challenged and each one is different; no-one learns quite alike. Adding a skill to learning quickly, learning to memorize quickly, visualizing pieces, learning a memorization routine that holds up, all are imperative skills.
The ones who never get ready, they will most likely not be ready later either; there's always something that comes in-between deadlines and busy schedules. As teachers, we are always challenged with these situations.
In all the playing requirements, I always insist on scales, chords, cadences and arpeggios. My students start these patterns in the very first lesson and after some short 3 or 4 lessons they show me how they manage to move their fingers running up and down the keyboard in scales patterns with accurate fingering. That always makes me very happy. They learn reading notes while learning to play. These early mechanical times are my GOLDEN TIMES with a student - they cannot yet play pieces and they are happy to move those fingers!
This is where I set my foundation for later on. Good habits, enjoyment of playing, moving the fingers nicely curved - oh wait - that's usually on my wish list and when I have parents who supervise I get nicely curved fingers. I always try to involve parent as much as possible.
So now, the Guild auditions are around the corner and we are on a strict schedule practicing diligently each piece entered a minimum of 5 times when very young and later on broken into sections with many more repetitions at various speeds, error-free. If an error is made the piece needs to be slowed down. The mind simply needs more time to think and it will be error-free if played slow enough.
That is the single most important habit to master that will take a student through any 10 - 15 piece program at any level.
And the second most important skill is scales, chords cadences and arpeggios - or maybe this is the very first utmost important skill to cultivate.
The book Play piano In All Keys Scales Chords Cadences Arpeggios Fingering Charts is the single most important book to have in any piano library. Without this book, I would not be able to take all my students through their large programs for their Guild auditions. And mind you, my students are regular honor students in school who also want to excel in piano.
Before Play Piano in All Keys Fingering Charts books, I would hand draw the scales fingering, now i just turn pages and the students love it, they can effortlessly master these skills time and time again.