The rule list allows only one action per item. For example, if I have a column for transaction type (Field = TransType) and the options available for this field using dropdown menu are "Cash", "Bank Transfer", "USD Cheque" and "HKD Cheque". Then, lets say I have a field named "Cheque#" which should be shown only if "USD Cheque" and "HKD Cheque" are selected as TransType.
So I create a rule that if TransType = Cash, then hide "Cheque#". Then I want to add another rule that if TransType = Bank Transfer, then again hide "Cheque#" but this time it won't let me select the field "Cheque#" as it has already been used once in the previous rule.
Now in this particular example I know there are easy ways to solve the problem, that is by creating one rule for both "Cash" and "Bank Transfer" fields together and then hide the "Cheque#" field. But this is just one example I am trying to illustrate. When you want to construct little bit more complex forms then this becomes a shortcoming.