Crescendos and decrescendos and other types of phrasing are abstract terms that generally represent increases or decreases in volume. While I still don't think you should know "when to use them," I do think that you should know about them, and other theoretical terms, like cadences and German sixths. Knowing about them and exploring them can strengthen your musical sensitivity because it exposes and impresses you with a wider variety of feelings.
Also, I think that when you consciously decide on using certain patterns, it's harder to improvise and come up with different interpretations to play.
If you have a microphone and want to converse about this with your piano at your side, add me on skype: raymondbliu
Also, I think that when you consciously decide on using certain patterns, it's harder to improvise and come up with different interpretations to play.
If you have a microphone and want to converse about this with your piano at your side, add me on skype: raymondbliu