This option for Go to layout is only useful within a script. It has no purpose as a single step option in Button Setup.
Say you have this script:
Go to Layout [Details]
Do stuff here
Go to Layout [original layout]
You can set up a button to run this script on a bunch of different layouts and they will all change to the details record, "do stuff" and then return to the layout where the button to perform this script was clicked.
Note: If you are looking for a "back" button that will take a user to the previous layout, that can be done, but not with the "original layout" option.
Regarding your bottom note, going back to the previous layout would utilize the summary/calculation funtions + variables?
Just a global variable or global field.
The script that takes you to a different layout first enters the name of the current layout into the field/variable. The "back" button uses Go to Layout with the "layout name by calculation" option to refer to the name stored in this field or variable. It's even possible to set up code that Builds a return separated list of the layout names so that you can have forward and back buttons that work much like the same buttons in your web browser.