With various kinds of VFX plates, it's necessary to de-noise them before working with them and re-grain them after the fact. Often this is to match grain on different plates, or better match paint work and tracked in elements.
Often times these plates are denoised by a VFX editor, who pulls them from the show's timeline of master files and transcodes them to dpx or exr to give to the artists. Now this Resolve 15 you can have the entire timeline in the same application and pull your own plates. Except right now the most robust de-noising tool takes place after the fusion tab, so it means plates that need to be denoised have to be rendered round trip and brought back into the program.
Seems it would be better to either bring the resolve denoiser tool into Fusion as a node, or allow clips to be brought in to fusion post color.