 The second category includes scores that are arrangements or transcriptions made after the completion of the work, usually by someone other than the composer.Piano–vocal scores are generally created to enable a conductor or choir leader to rehearse the singers with a piano accompanist before the choir begins rehearsals with the orchestra.The cost of rehearsing with a professional orchestra is so high that choirs typically hold a number of rehearsals with piano accompaniment to prepare the choir, as the cost of hiring a single piano accompanist is much lower than hiring 50-100 orchestral musicians.