dante01 as someone who is knowledgable regarding all things audio/HiFi etc i thought you may be interested to know of my practical example of what can happen if an isolator is not fitted.
Some years ago (NTL days) I had to call an engineer out to carry out some work and he for some reason removed the isolator from the incoming coax.
After he left I could hear a 50hz mains hum from my sub connected to my Yamaha RX V3087.
As you have probably guessed it was caused by the removal of the isolator and hence in doing so it caused a hum loop in the system.
Fitting an isolator cured the problem.
So they do have there uses but not necessarily for full on lighting protection.
The isolator is mandatory and not optional. An installer is obligated to fit one or ensure one is present. They are not intended to prevent damage associated with lightning strikes and this is not why they are used or installed for.