is / is not equal condition will allow you to use individual mapping methods for individual products or product groups. You can assign some values to products depending on what the value is equal to (or if is not equal to).
You can use this option to set the value Red, if the source's color attribute is equal to Red. If it isn't the value Blue will be set.
It is always recommended to have a Fallback rule for products that are not matched by the condition, just to make sure that there are no empty values in your output feed.