It allows different teams to write in different languages, have different deployment cadences and different testing mechanisms.
The overhead of network calls and its attendant problems can be a worthwhile price to pay if you need to loosely couple your teams.
This is why my yardstick of "should it be a micro service?" is "could it work as an entirely separate business?"
I was a massive skeptic of micro services until I saw that it actually solved some people problems pretty well despite incurring a technical cost.
I'm pretty convinced it's an anti pattern in small startups though.