If an outline is getting large, you may want to archive pieces of it.
It works by converting a sub-outline into an include.
Only archive sections that you don't need to edit, because you won't be able to edit them.
For example, if you're keeping a blog in Fargo, you might want to archive July's posts at the beginning of August, only if you're sure you won't need to edit them.
Put the cursor on the section of the outline you want to archive.
Choose Archive outline from the File menu.
Click OK to the confirmation prompt.
Wait a few seconds.
The bar cursor should change to an include node.
The archives are stored in the archive sub-folder of your Fargo folder in Dropbox.
They're stored in a calendar structure and given fairly cryptic names that are very unlikely to "collide" with each other.