I'm guessing they are referring to real-estate capacity. Not including space junk there are about 2,300 satellites in orbit. This is quite a proportional increase and the risk of collision with junk will go up.
The collision risk will depend very much on the altitude at which they are placed... this is also a big determiner of design life (N years before the orbit decays and they come back into the atmosphere) and might also have some effect on signal strength / geometry.