As a second thought, that makes some sense. Regional offices do localization, sales (with support), and legal adaptation mostly. Any company that wants to sell on several countries need such stuff.
More than a hundred employees for each office looks oversized, but not extremely so.
The only question yet open is if Twitter needed all this infrastructure to become a viable business, of if they could open smaller and grow into that size organically. But well, even if Twitter didn't need it, it's reasonable to imagine that some business would need it.
I guess my question of what a company could spend 1 billion of investment on is answered.
"Twitter has over 4,100 employees in more than 35 offices"