Hi Phil,
GoPro Studio was originally developed by Cineform, before GoPro bought Cineform.
Cineform specialized in intermediate codec when computers were still "slow" and expensive.
If you use GoPro Protune and setting white balance in Native and Color in Flat, the power of Cineform codec will be most useful. Yes, its very big file when transcoding from GoPro MP4 to Cineform mov, because its so much less compressed and its a 10 bit file.
If you are a Dive Master as in a diver, it is very hard to beat the ease of color correction a Protune + WB Native + Color Flat for underwater video. Underwater video is the worst of the worst when in comes to original color being destroyed by water depth. It takes time to practice but the freebie GoPro Studio as a color correction software is easy to use. I only use GP Studio for the sole purpose of color correction of UW video. For land video I do not mix much between different cameras, so I do not ever need GP Studio transcoding feature. I also do not use GP Studio for editing, its too simple a tool and not flexible enough
Even though GoPro original MP4 is an 8 bit file, when being transcoded it becomes a 10 bit file and you have finer adjustment to play with. Its like having setting of 256 levels of shades to suddenly becoming 1,024 levels.
Surely starting with a 10 bit camera native is better, but this is not bad at all for a freebie and its actually a professional codec that Cineform is.
The true beauty for me using Cineform is, it is the only free of charge codec I know ( my knowledge is limited ), which you can mess with original file colors and that original file remains a "virgin" file forever. Other files when you start messing with the color, you can only get to see the final result after rendering, not for Cineform. GoPro Studio also works parallel with other video editors, example Vegas Pro in real time. Mess with color in GP Studio, the result immediately visible on Vegas Pro. Mess with the color as many times as you want, Cineform file remains virgin while the colors already changed.
Have fun editing....