One of the the core differnences between New GL and Glassic Gl is online integration of items like PCA,segments,Business area etc with GL.
In classic GL we need to do a lot of periodic closing activities to get restricted Balance sheet at these levels.
with online document split enabled in New gl these periodic activities are gone.
Differnce between business areas and segments:
both can be used to draw financial statements at other than co.code level. But for segmental reporting you need to have PCA as segments can be derived only thru Profit center. (BADI available in other cases)whereas Business areas are cross co.code settings so you can assign them to sales area/plant/divsion combination for derivation which remains the same as classic gl.