File Naming
The first choice we need to make is simple: Rename To or not.
If we choose not to rename the exported files, they will have the same name as our source files. The remaining functions in this tab will be unavailable, and the only choice we can make will be between the uppercase and lowercase extensions. You might have your reasons to change from the default lowercase to uppercase, but I always leave it as is. It is one of those Lightroom options I have never changed since I first used it.
Suppose we, however, choose the Rename To function. In that case, we are not only welcomed with a great selection of renaming presets but also a fully customizable File Template Editor. Once we click on the list of options, we will see seven presets: four that will use our set Custom Name and three that will use the original filename. I usually choose Desktop and the same name for Put in Subfolder and Custom Text when exporting images. This way, I can keep track of what goes where...