You have a situation where a business process works only for a particular condition. You can design your logic by putting the IF condition for that functionality. For example, we had a requirement where payment term was determined for one sales area, customer and sales order type. We could have achieved this requirement by just putting a condition(using hardcoding) on sales area, customer and sales order type. But instead we used a custom parameter table for this requirement and maintained one entry in the parameter table.
As we all know, the business scenarios keep on changing and now the business wanted payment term determination for 190 different combinations of sales area, customer and sales order type. The client was delighted to know that no code changes are required and also no need to import a new Transport Request to production environment. By just maintaining entries for different combinations in parameter table, the functionality of payment term determination worked !! The development efforts, time and cost was saved dramatically.
Using parameter or constants table while developing SAP ABAP programs is a very simple technique to avoid hardcoding. It is a best way to make the code reusable and to avoid rework. It also keeps the code simple and robust. You can create custom parameter table or use the standard parameter tables like TVARVC.
Next time you have to put any such condition, you should use the parameter table. You will be amazed to see how efficiently you can make the functionality reusable and flexible !