The Simultaneous Ringing feature enables your virtual number to divert calls to a maximum of 10 different phone numbers, even if they are located in different countries.
These numbers will ring in unison. The network automatically connects the call to the first number that answers.
Is this a useful feature for you? It could be, however most customers probably have less of a requirement. Perhaps 3 or 4 numbers is what the normal customer requires.
But some customer do use this feature to because they have a widespread network of call centers and the calls may be crucial to be answered by a human. Or a customer may have very important calls and simply wants the calls to follow whatever phone number he/she may be near at the time.