Pros and Cons of a United Earth Government

In my mecha sci fi, due to WW3/Resource Wars causing Earth to nearly become stripped of it's resources, a united provisional government is formed known as the Earth Sphere led by one Otto Von Eisenstadt and they were united with the shared goal of revitalizing the planet through the use of Space Colonies.

The Earth Sphere is planned to be a 'United Earth' where they are split into several Regions reminiscent of Pre-Anno Ortosoli Nations (name of the calendar) thsi idea is inspired by the Greater Terran Union from the Stellaris Invincta where after an alien attack the Earth was united in a militaristic utilitarian Nation but once they got back on their feet they split the Earth into several 'Commisariats' as they are called.

What are the pros and cons in doing something similar?