Reflectance maps take a very long time to generate, and if you are working with multispectral imagery typically there will be many channels (e.g. Sequoia), or several cameras (e.g. 3 Canon S110 cameras for the eBee). It would be great to choose which reflectance maps to generate in order to save time.
Example workflow: I want to calculate the Enhanced Vegetative Index (EVI) which requires NIR, red, and blue bands. My project contains all 3 eBee cameras to cover all the required bands, plus the RGB to get a visual ortho for inspection. That means I need to generate 9 reflectance maps when I only actually need 3. Selective reflectance map generation could cut my index map processing time in half!
This would also be extremely helpful when the reflectance maps need to be regenerated which happened to me right before a deadline. The maps appear in the index calendar but Pix4D still says I needed to generate them. I had to do this for 4 projects/acquisition dates, meaning I had to wait 6+ hours per project just to get 3 bands.