A column can be defined as SPARSE column in SQL Server Version 2008 and above. This would give advantage in terms of memory occupied , if the value stored is NULL.The space saved may be 20% to 40%(msdn).
The below data types cannot be marked as SPARSE:
Text,NText,geography,geometry,timestamp,image and user defined data types.
Below are the example:
We are trying the compare benefits of using SPARSE on table with CHAR data type columns and table with VARCHAR data type columns.
We have additional overhead in fetching the NON-NULL values of SPARSE columns.
So,analyse and based on the amount of benefit ,proceed with SPARSE columns in a table