The ONLY reason I would ever have multiple BE files would be if you reached the 2 GB mark and had to grow more (and for some obscure reason could not upgrade to SQL Server or ORACLE or something else that doesn't have the 2 Gb limit). I can imagine that you could have some oddball security requirement for this, perhaps, but it would have to be so contrived a case as to not be practical for most of us.
Further, judicious archiving, deletion of archived records, and file compact/repair operations would at least push back the time at which you would need to do a two-for-one BE split.