The main reason to use microspectrophotometry is the ability to measure the optical spectra of samples with a spatial resolution on the micron scale.  Optical spectra may be acquired of either microscopic samples or larger samples with a micron-scale spatial resolution.  Another reason microspectrophotometry is useful is that measurements are made without destroying the samples.  This is important when dealing with stained/unstained histological or cytochemical biological sections, when measuring film thickness in semi-conductor integrated circuits, when matching paints and fibers (forensic science), when studying gems and coal (geology), and in paint/ink/color analysis in paint chemistry or art-work.