TauKay Edizioni Musicali has a large number of free-to-download scores online, yet another example of the way the winds are blowing for sheet music. While there will likely remain a role for sheet music printed on paper and physically delivered to musicians and libraries — and a particular niche for elegant editions — the time and cost efficiencies of direct downloads are increasingly hard to ignore. Sheet music, on its own, for new and experimental music, is not an especially profitable business, the larger profit is in commissions and licensing for performances, broadcasts, and recordings; sheet music is an instrument in realizing performances, broadcasts, and recordings. If traditional sheet music publishing is either slow or expensive, it runs the risk of leading to fewer rather than more performances, which makes publishing more of an obstacle than an assist to the music.
Sheet music in the form of scores and parts for choral groups, bands, and orchestras which becomes widely used (especially by educational institutions) can be profitable as a sale or rental operation. The individual composer must decide whether he or she can handle such operations on their own, the profit expected covering his or her costs in time and materials, or be willing to share license fees in return for allowing a traditional publisher to carry and promote their work, or to go the download route instead. At present, I can well imagine many composers using a tactical mix of publication methods, with solo and chamber works largely issued online and ensemble works intended for institutional use promoted via online perusal/study scores but available as rental or purchase sets of scores and parts.
One reminder to performers: if you download a work and perform it, identify the piece accurately on your program and also let the composer know about the performance directly. In many cases, institutions pay blanket fees for to licensing organizations, so the particular performance will not cost you anything more and the main obstacle to the composer from eventually getting her or his fee is a lack of reporting. Reporting is the least that you can do when the composer has provided the performance materials for free.