I use a custom field (Work, oddly enough) to organise pieces, but I use other custom fields; 2 additional genre fields, Orchestra, Chorus and Soloists. When I started doing this (about 14 years ago) conductor wasn't a standard tag, I don't think Composer was either. The ability to define custom fields and arrange views which used them is why I use JRiver and continue to do so; I haven't come across anything else that approaches the functionality that JRiver has.
Genre has very few options, for music it's basically Classical and Pop. The extra 2 genre fields are used to organise music with more granularity. In my case I use Chamber, Choral, Opera, Orchestral, Solo Instrumental and Vocal as the secondary subdivisions, then they are grouped by composer. (I have another sub genre for Collections for albums with multiple composers works.)
These view schemes let you find the original albums easily, but there are other view schemes which are organised by composer, conductor, orchestra and soloist which lets you find any piece very quickly and easily.
Unfortunately the non standardised tagging makes organising classical music a lot harder work than pop music is; the metadata that JRiver finds is hugely variable and most of the time needs a lot of editing. Genre is a case in point, a lot of CDs use Classical as the genre but there's an awful lot that use any random sort of variation you can think of. For instance, many of the Mozart 225 CD box have a genre of Mozart, which I find very silly.