I have heard that extreme high resolution is not always a good thing specially when it comes to low-light performance. On the other hand, since the size of the image gets larger, it may need higher buffer for contentious shooting which slows down the performance for shooting sports. However, I've noticed that both Canon and Nikon have already decided to go on a mega pixel race as the 5D Mark IV has gone to 30 MP and D850 has gone over 45 MP, not to mention Sony that pioneered high mega pixel cameras.
Considering D750 or D5 or 5D Mark III, would it be really worth to upgrade from these cameras to the new high resolution models? Is that extra resolution something very tangible?
On the other hand, if high resolution is a good thing, why the high-end full frames are kept at max 20 MP (D5) of even 12 MP (A7S II) ?