File size smaller after saving

I’m new to access.
- I saved my first database and it was 2,176 KB
- I saved the same file under a different name and got 704 KB
- I saved that newest file under yet another name and got 528 KB
- I repeated this twice more and got 548 and 534 KB.

Is this anything to be concerned about or is Access just compressing the file? If the latter is the case, why does Access do this only when I save the entire file, as opposed to when I save the individual objects within it?

Thanks