More information means higher quality, but also a bigger file size. Works the same the other way around (lower rate, less quality, smaller size).
It's a matter of testing by yourself and finding the right amount for the quality you want and the rig you have. Too high and the disk might bottleneck it or your GPU might not be powerful enough, but too low and you'll have a crappy quality in the end.
Going too high also has diminishing returns, so there really is no way for you to exceed there.
GVR makes it easier for you by defining "Megabytes per minute" anyway, so you have a better idea of the final size.
When I used to test GVR, it was about 4~4.5 GB for 15 minutes of 60fps recording, 1080p resolution at...250~350 MB/min, i believe? Can't remember right now and can't check.
Very crisp quality, audio slightly off-sync (likely because I was playing at 90fps and recording at 60fps, COD AW)