Consider the scenario:
A business scorecard has to be implemented using Rules. It will have varying conditions and based on each set of conditions satisfied, you would want to add a factor to the score. Now, how can you keep a track of all the counts?
Ofcourse, setting the "Return Multiple Matches" property to True and "Rows are Mutually Exclusive" to False, will ensure that multiple rows are evaluated and actions are executed for the satisfied rows. But we also have to ensure that the values given dont get overwritten, instead are added on. For such a scenario, ability to write expressions as an action in the decision table helps. Here is how you can do it. Press "F2"/double-click on an action and press "Space"/select a value, to see the options of adding an expression, open and close brackets along with a list of parameters you can use for forming the expression.
Here is a sample screenshot:
