In case it is useful to anyone, here is comparison of a DJI P4 multispectral flight processed with the different calibration options:
(1) Cam+Sun
(2) Cam only
(3) No calibration
This link (Terria Map) shows the Cam+Sun and Cam only comparison. If you turn off one of those and enable the third data layer you can see what it looks like with no calibration (apologies for the map error when it loads, the platform is still in beta 
).
To my untrained eye I can’t see much difference between the first two settings, but I haven’t done any quantitative comparisons and I’m not actually sure what one could use for a control unless you had micasense data of the same flight to compare it to, or something like that?
Anyone done any more robust testing on this?