Most have sound also, which is a definite advantage. If you can't see all of the cages, you can hear and sometimes catch birds fighting before it is too late. You can run an extra 30 or more feet of wiring into the aviary and move the camera to any cage for viewing. I have my veterinarian annually check all my birds. When production drops, or you have increased infertility or dead in shell, you know you have a problem, so then you call in the vet.
Preventive medicine is the key here.
Once you have any of the above problems, it is too late in your breeding season. If the veterinarian is called in and treatment needs to be done, you may even lose the second half of the season. In addition to illness, there is now disruption among the entire aviary due to catching birds and treating them. Over the years, in discussing disease and breeding with other aviculturists, it has been amazing how just a good going over the birds and treating for seemingly minor problems has helped many aviculturists realize the breeding potential of their birds. Oftentimes a good breeding pair may start bickering with each other, and we find out one of them has a low-grade infection.