Currently "by design" the getSamples method of an image service provides the functionality to get pixel value of the data source by a single point, or multiple points along a polyline or inside a polygon. This is extremely helpful for example to create DEM profiles.
Nonetheless this functionality would be also helpful for image services published with raster functions.
Other functions like identify or exportImage support raster functions which were attached to the image service by raster function template with a special parameter renderingRule. Functions like computeStatisticsHistograms natively respect raster functions attached to the referenced mosaic dataset.
For now we can use Identity but imagine the case you want to get 100 points/samples along a polyline on a mosaic dataset image service with raster functions. This leads to 100 identify requests instead a single getSamples request.