I mean the file is zipped, as in compressed. So it might just look like a file, but if you open it inside the zip (with file explorer) Windows does have to decompress the file in the background to show it to you.

Which is obviously slightly slower than if you unzip the file and put it somewhere and then open it, but you won't really notice the difference except we're talking about massive files.

And of course if you make changes to the file you can't save it (except to a new file) as it gets opened up as read only.

If you just want to store the file and view it every now and then I don't see a reason to unzip it. And you can always do that later anyway.