Imagine you have a growing consulting firm. Other than yourself, you have 4 employees -- a business manager, 2 account managers, 1 billing specialist. You're not planning to share an office, as everyone is working remotely from their homes. (You hired people you trust, from prior gigs, so you're comfortable with a virtual office.)
While planning your business venture, you've been giving out your personal cell phone number, but now that you have client-facing employees who also deal with vendors, partners, etc., you want a unified business image, which starts with a single, centralized business phone number. Since you don't have a physical office, you've been exploring the concept of a cloud-based phone service that allows you to assign simple extensions to your virtual employees stemming from your main business line.