There are a number of limitations to business rules including
There is no support for RegEx expressions
No support for OR conditions.
You cannot hide a section, sub grid, etc only fields
Does not work on mobile forms only web and tablet.
Also for each typical rule you will probably need a reversing rule. So in my example if the revenue is over 50,000 then the account is changed to a preferred customer however I also needed to add a rule whereby if the revenue was changed to below 50,000 it was reset. As you can imagine you could end up with a whole series of business rule to set and unset fields and values.