In our area the electric utility is leery of mounting a service on a building that is "mobile", or that may not be of a certain level of structural soundness to bear the strain of service cables, ergo, for "single-wides" and units that may have lighter weight structure than standard 2x4 studwalls, a separate pole is required.
As for extra circuits it is common here for those to serve an exterior well-house perhaps, or, in the case of a street-legal 100 amp service for a dwelling, to serve a self contained heat pump without gobbling up too much of the building's load.