If you can read your piano music, why memorize it?
Alternatively, when you have your music memorized, do you need to look at the score anymore?
There is a distinction between sight-reading and playing learned music using a score. When you learn a piece using written music, what you are actually doing is building memory and associating it with the visual on the page.
This is still technically a form of memorizing, but it takes far less time to develop compared to fully memorizing a piece.
If you choose not to memorize each piece, you will generally spend less time per piece and experience more pieces as a result.
There are many situations where it is more appropriate to memorize:
You may be required to memorize for recitals, auditions, and exams.
You will find it necessary to memorize extremely fast pieces.
Memorizing helps if the music is above your level or difficult to read.
If you enjoy "collecting repertoire" and wish to play your music in any setting, you should memorize.
Keep in mind, small musical details will slip away over time. You should still check in with your scores to keep your pieces in good shape.
If you choose to memorize, you will spend more time on each piece and the performance standard will be higher as a result.
Throughout your musical journey, you will find that both reading and memorizing have their place. You can even memorize the difficult passages of certain pieces and read the rest, or you can commit to memorizing.
Strong reading and memorization skills are ultimately necessary to becoming a fine musician.