A decade ago, international phone calls and SMS would have cost me an arm and a leg, and there's really no equivalent for Facebook which lets me keep in touch with the lives of people I care about on the other side of the world.
Yes, there was email but that doesn't really substitute for the short low-latency, ubiquitous worldwide communication of WhatsApp (and it certainly didn't 10 years ago when it was largely tethered to a desk) nor the ability to keep up with my friends unsolicited that is Facebook (what am I supposed to do, ask all of my friends to write me an email of what they're doing once a week?)
Are global migrant workers an edge case? perhaps. But while forfeiting FB and WhatsApp wouldn't make me a hermit, it would certainly make communications with my friends and family back home to be lesser in number and richness.