Composers, as craftspeople, tend to overemphasize the professional, the formal, the finished, and the perfected. However, a lot of useful and valuable music-making is not professional and not yet formal or finished, let alone perfected, and this emphasis can often be a distraction from opportunities for music-making — indeed most music-making — in situations, environments and on occasions which may well be informal, provisional, and yes, (cheerfully) far-from-perfect.
New music, in order to thrive, has got to go wide and deep into our musical culture, an established if dynamic presence, emphasizing not only the most prestigious occasions and institutions and requiring only the most virtuoso musicians. This means music for amateurs, music for children, music for pedagogy, and music for private use as well as civic and institutional functions.
Fortunately, we have some very good models of composers writing pieces designed to reach wider sets of players and audiences which are nevertheless integrated into their work as a whole. For example — and looking only at piano music (we could as easily look at vocal music or music for guitar or recorder or school instrumental ensembles) — the collections of small-scale piano pieces by Bartók — most famously the six volumes of Mikrokosmos — and, later, Kurtág's Játékok (Games) and transcriptions for piano two- and four-handed, or Virgil Thomson's two collections of piano Etudes and the large series of Portraits. Mikrokosmos was compiled initially as piano lessons for the composer's son, Péter, but grew to be a progressive collection, varying from sketches to substantial pieces, illustrating nearly all of Bartók's technical concerns as a composer and pianist and in many cases serving as a sketchbook for other concert works. The Játékok includes repertoire intended for private and public use by the composer and his wife, occasional pieces for friends and colleagues, and, like Mikrokosmos, preliminary and intermediate steps to major concert works (the various metamorphoses of the enig- and emblematic Virág az ember materials as particularly fascinating.) Many of Thomson's Portraits, likewise, find their way into substantial concert works, often orchestrated, but the origins, as portraits of named persons who sat for Thomson in the manner of a portrait painter, were opportunities for the composer to experiment without the pressures of the formal, finished and professionally polished, often executed in the kind of automatic writing that, despite Thomson's insistence on his professionality, indulges in the advantages of — as Buckminister Fuller put it — daring to be naive, echoes the practices of modernists in other disciplines (i.e. Stein, the surrealists), and reliably delivered Thomson his most interesting music.
Among more recent examples of the usefully informal, I would add the scores of exquisite small-scale piano pieces by Gordon Mumma (some of which are available as scores from Material Press, and the recent double cd of these, played by the great Belgian pianist Daan Vandewalle is highly recommended) and also mention Lloyd Rodger's The Black Book, a project of composing approximately a piece a day for year, in ink without edits. (I haven't seen the scores, but I believe that they are in open score form, again, a very useful idea.) This seems to resonate with Lou Harrison's suggestion, for the "stuck" composer, of composing a whole piece each day, every day: the idea is not to try and write perfect pieces, but to practice writing performable complete pieces, however small the scale or modest the ambition, to concentrate and focus and practice craft, allowing the ambitious, formal, polished, and perfected to emerge on its own terms.