DBO format is DarkBasic's internal format. ALL files that it loads are converted internally to this format before use. If you use .DBO format your objects will load faster than if you were using a different format, this is due to the engine having to copy all of the data from whatever format to the .DBO structures.
There are no limitations to using .DBO format as opposed to any other(besides those imposed by the engine). You will run into difficulties if you have hugely complex object structures in the file regardless of the format being DBO or X or any other format.
If it ain't broke.... DONT FIX IT !!!