Your tax return is in a data file ending in .tax2019 or .tax2020, etc.  You can download it (and should) if you want to open it in the Desktop CD/Download program like if you need to finish a prior year or amend a prior year or you want to switch to the Desktop program. 

You can also save your return as a pdf file.  You should download and save both the .tax2020 file and pdf files to your computer when you are done so you can access it after Turbo Tax Online closes each Oct.  and you can't get a copy.