I'm a musician and composer myself (even used to work as a professional musician a couple of years). There are totally different approaches to composing music, from totally intuitive/non-intellectual to totally formal/rule-based. I would say that today the majority of composers compose music intuitively and directly on the instrument, without being aware of the exact processes involved. Formalizations in music are therefore mostly academic, arising from analysis of the compositions of others, as an attempt to explain how these compositions work. For algorithmic composition, such formalizations are necessary, but so far not sufficient to create a high-quality composition (just as one could not become a good musician just by studying music theory). Nevertheless, it is necessary to study such formalizations if one wants to advance the field of algorithmic composition. However, I consider most "classical" approaches to formalizing music obsolete for this purpose.