You may have a script that you want to run from several layouts. No matter where it starts from you always want the user to go to another layout, do something, then be returned to the layout they started from. Instead of having to positively track where they started and returning them there, you can simple include the final script step 'Go to Layout [Original]'
Ae you saying the "original layout" only works in a script, and that it is the initial layout in that script?
Why is it an option on the button format?
All the button settings are really single script steps. Some options for these settings are only useful if the step is in a multi-step script. Go To Layout have its options modified to specify a specific layout or a calculation that evaluates to the name or number of a layout. These other options will work as single step buttons settings.
FWIW, it's good practice to set up all buttons with the Perform Script setting and then write a script to do what is needed--even if that script is just a single go to layout step. A button, with it's settings, can be copied and pasted to multiple layouts. If you use perform script for it and then later determine that you need to change what it does, you open the script definition and edit the script and then all your buttons will employ the updated script. If you use one of the other settings for such a button, you have to go to each and every layout and make the same change to each (or copy and paste the changed button all over again).