James Taylor wrote a nice blog post identifying some of the criteria that hints at the need for business rules.
- Lots of rules required for each decision
- Presence of complex inter-dependant rules
- Behaviour must change often
- The rules require business expertise to understand
- Business users insist on controlling the rules
Those are definitely good indicators of the need for business rules.
Read James Taylors original article at: http://jtonedm.com/2009/05/14/heres-how-you-know-you-need-business-rules/