Hello Manaswini,
Another illustration-
Attributes with data type Timestamp can be used as time reference attribute in planning area.
For eg- You have an attribute as data type decimal and another as data type timestamp assigned in a master data. When you assign this to a planning area, you would make decimal type attribute as key figure and select timestamp type attribute in 'Time reference attribute' column.
When you see this in planning view, you can see the attribute as key figure only in the time buckets for which timestamp attribute is populated in master data for a particular combination.
Thanks,
Rohit