Reference

Call forwarding is an easy way to avoid disruptive phone calls during meetings and conference calls. But it can also be a convenient way to divide your workday into the parts when you are available and the parts when you need to sit focused and work. If you have a manned switchboard, it also makes it much easier for your receptionist to know which people in the company are available for calls and which are not.

It's also a way to work more efficiently if you schedule your references. For example: mornings are for focus, and during that time, all calls can be directed to a receptionist or voicemail. Notifications about calls during the focus mode are up to the user to decide.
With references, it's also easier for those who handle a lot of calls. They can see right away on their mobile phone, computer, or tablet if you're in a meeting, busy, or gone for the day.