By default, an object file can hold up to 65,279 (almost 2^16) addressable sections. This limit applies no matter which target platform is specified. /bigobj increases that address capacity to 4,294,967,296 (2^32).
Most modules never generate an .obj file that contains more than 65,279 sections. However, machine-generated code, or code that makes heavy use of template libraries, may require .obj files that can hold more sections. /bigobj is enabled by default on Universal Windows Platform (UWP) projects because the machine-generated XAML code includes a large number of headers. If you disable this option on a UWP app project, your code may generate compiler error C1128.
For information on the PE-COFF object file format, see PE Format in the Windows documentation.