LookUp - is similar to Obj-Open, if you are passing primary key of Work-Object (or) data instance as an input to data page, it will pull all the data related to primary key and hold it in data page cache.
Hi @AbhishekC1725: Purpose of savable data page is to fetch data from SOR which can be updated by your business logic and update it back to the SOR. If you remove the data source, there is no option for the data page to fetch data. If you remove the save plan, there is no option for the data page to save the data back to SOR.
Please see this for details about savable data page.