Why did fixed orchestra personnel give composers more freedom in orchestration?

The standardization of orchestra personnel, such as the ensemble established by the Mannheim school, provided composers with greater freedom in orchestration by eliminating the need to write music that could be performed by interchangeable or unspecified instruments.12

Prior to the mid-18th century, composers often could not rely on a fixed group of players and were forced to write parts that were flexible enough to be played by various instruments. The prevailing contrapuntal style of the Baroque era generally involved simply assigning available instruments to a musical line, provided the notes fell within the instrument's range.2

By establishing a consistent, fixed ensemble, composers were no longer constrained by this uncertainty. This stability allowed them to experiment with the specific capabilities, tone colors, and technical agility of the instruments within the group. As the musical style shifted toward a focus on melodic invention supported by harmony, composers could move musical motives between specific sections and instruments, treating them as distinct entities to create new facets of orchestration.23