I believe you are talking about one of our best practices. The idea is to always have a clean clipboard, so if your activity is using a working page to temporarily store information, it is best practice to remove this page at the end of the activity. Firstable because you don't want to work on another case, reach the same process and use an already existing page which may have irrelevant information (from previous case). Also, removing unnecessary pages will always improve performance.
I agree with Marc. Although, you don't need to create/delete the page if you don't actually need it. If all your activity does involves work on existing data/pages and you don't need a temp work area, then don't make the page. Likewise, if you are building a process that passes some data around for a few activities and is purely encapsulated in that process, you can have the first activity in the call stack create the page, and then delete it when the stack unwinds. You may want to make a comment in the usage notes of all the activities indicating where your page comes form and how your activity should always be called by the parent activity/process so that a future developer doesn't pick up one of the later activities and get into trouble.