People calling from company phones, but wanting callbacks to the switchboard.

People with multiple phone cards, but wanting callbacks in one place.

People with phone numbers belonging to another country.

Doctors responding to out of hours requests, but not wanting to share their direct contact.

One legit use is for companies/organizations that have a PBX (Private Branch Exchange) where each desk has it's own external telno. They can make all the calls appear to come from the corporate main number. So instead of 415-555-9xxx for whoever's extension it shows up as "415-555-9000". This is useful for both not revealing a personal extension and for branding

Of course, why it was designed to allow spoofing of any number in the world, instead of only numbers in the same block...

Any business with multiple outbound lines might find it handy.

There’s probably a better solution.

Think of every company that wants all outgoing calls to show the same phone number. Not just call centers, but also doctor's offices, corporations, and even the mechanic down the street.