This is going to be a short one. Just like the original a7S, there is a resolution loss when you shoot at 50/60p in 1080p as compared to 24/25/30p. Here are two images you can compare (stills taken at the frame rates mentioned, no processing done, click to enlarge):
1080p25 (XAVC HD)
1080p50 (XAVC HD)
Takeaway
If you are cutting between 24/25/30p and 50/60p, then you might have blur the sharper footage or sharpen the 50/60p footage so they match.
There is a clear loss in resolution! Possibly this is one way Sony tries to maintain the prices of its more expensive video cameras.