When choosing a format for your Generated Report, consider the benefits and limitations of each file type.
For example, Excel files can be versatile and allow you to work with your Report data. Acrobat Files may offer the most visually pleasing format when presenting your Report to others.
(An added bonus of XLS files though, is that most versions of MS Excel or Apple Numbers will allow you to create an additional copy of your Report file in CSV format, any time you want. Something that doesn't work as well with the other formats, going in the opposite direction.)
As long as you save your Layout in the LMS, you can always reload your Report and then generate another exportable file again, in any of the other formats Absorb offers. The information though in the LMS may have changed since you last generated it.
If it's full of different data, you might be only partially able to bring it back to where it was by applying a Date Filter (and only if data has just been added to the LMS, and not changed or removed). Just another reason to choose an XLS file whenever you're ever in doubt of what you'll need.