Cleaning up old functionality such as unused variables, fields and functions makes your code and objects better readable for other developers but can be risky if you remove too much.
The where used functionality can help you with this task. Let's take a look at table "BizTalk Reservation Entry". This table has all the right ingredients for a nice example!
It has 9 unused variables, 1 unused field and 2 unused functions.
With this information you could go to the Object Designer and remove them by hand but it's also possible to delete them straight in the where used functionality. Simply select the entries you want to delete and press F4.
This can be done with keys, fields, variables and functions.
If a field is removed the OMA will first delete all present data in the table and then will remove the field.
Look at this demo on YouTube!