In the Timbre category one will observe tuning systems/esthetics/composers where I find that microtonality is used mainly to realize certain timbres. Pitch and scales is of less importance.

A term describing the tonal quality of a sound; a clarinet and an oboe sounding the same note at the same loudness are said to produce different timbres. Timbre is a more complex attribute than pitch or loudness, which can each be represented by a one-dimensional scale (high–low for pitch, loud–soft for loudness); the perception of timbre is a synthesis of several factors, and in computer-generated music considerable effort has been devoted to the creation and exploration of multi-dimensional timbral spaces. The frequency spectrum of a sound, and in particular the ways in which different partials grow in amplitude during the starting transient, are of great importance in determining the timbre. 

Timbre, Grove