Known as "primer wars" in the RV community, are the debates regarding priming and painting of aircraft.
As we in Scotland live in a maritime climate, my inspector recommended priming of all aluminium parts, and sealing of metal-to-metal joints. As the aluminium is "alclad", arguably this is an overkill. Either way, the plane is likely to outlast me. But, in part, I was in this to build some skills, so I elected to go the whole hog and do the job "properly". You can see my notes on painting as I work through the project.
Worth noting is that priming has added 10% to the effort to complete the plane.