The Supplier Purchase Planning Grid holds a lot of information, not all of it is relevant to your process. You can add, remove, and move the columns as you can in any report, and you can save those changes for future use.
After you have made the changes you want to the grid, Click on Tools above the column headers and then on "Save view".
Then, fill in a name for the view and click on OK.
When you want to use this view on a new PO in Supplier Purchase Plan, click on Tools, Load view, and choose the view you want to use.