kapustinsane 1. Purely pragmatic/practical: If I ever want to "pull a piece out of my pocket" at a public piano or something, and I don't have my iPad with me, then of course i need the piece memorized.
This is basically the only reason that I would try to memorize something these days, and even then, I’ve found that I can (sort of) read the score from my iPhone. When I was traveling overseas last summer, before my trip I made it a point to practice playing a semi-memorized piece from my iPhone. Because the iPhone is so small, I felt like I couldn’t really “read” it from the phone, but having the score there on the music desk helped me focus my attention and not worry about memory slips. And I did end up playing that piece on a public piano that is available at Haneda Airport in Tokyo, so that was fun 🙂
2. Performance: I also feel like performing a piece at a recital typically calls the performer to have the piece memorized, but I don't know if this is true or not. Most professional performances I have seen by piano soloists are done without sheet music. Correct me if I'm wrong.
Professional solo pianists do tend to perform from memory, but IMO there’s no reason for anyone, especially hobby-pianists, to feel like playing from memory is a requirement just because it’s a recital. It’s really up to the pianist.
3: Internalizing them (this one might be the most important), becoming "one with the music", and pure joy factor. The pieces I have memorized in the past are the ones that I grew to perform the best, since I internalized them. By memorizing them I also gained some insight into their structure. Finally, when I have a piece fully memorized and internalized I am able to focus on the expression of the piece, without dedicating brainpower to reading the notes. In my experience, memorizing forces you to integrate the fingerings mechanically/intellectually, freeing up some emotional power.
To me, this is the most compelling reason for memorizing that you’ve stated. Personally, I don’t find this to be the case for myself. IOW, I have never felt that keeping my eyes on the score detracts from expression or from my experience of the piece. Also, I feel like I internalize the piece, its structure, the fingerings etc., even though I am also continuing to rely on the score. For me, by the time a piece is polished, the score is an aid and perhaps even a crutch, which is a word with a generally negative connotation but I’m ok with that in this context. And maybe I wrote this above, but I find that having the score is actually freeing, because I don’t have to worry about memory slips.
But again, this is very individual and I am very “score-oriented.” I also think it has to do with how I started as an adult beginner, and how comfortable I’ve always been with score-reading. But for you, especially since you mentioned the joy factor, if memorizing will bring you more joy when you play, then I think it makes sense to figure out how to memorize. And since it sounds like you regularly memorize other pieces, then you are probably more of a “memorizer” than I am.
In contrast, I can play many pieces quite well with the sheet music, but I feel like I am somehow limited in my ability to simply channel the music and embody the full emotional expression when I play them.
Yes, this alongs with the other things you posted, so I think for you, figuring out how to make memorizing this more complex music makes sense.
But then, maybe after you’ve done all you can to memorize it, if it’s still “shaky,” you might consider a hybrid approach, where you have the score out and you loosely follow along but don’t actively read it… this requires its own kind of practice btw, because if a piece of music is more than a page, you do have to actually follow along because otherwise your eyes won’t know when to go when you need to actually read something.
BTW do you read from paper scores or tablet/digital scores?