A Better Finder Rename’s user interface and default settings are optimized to give the best user experience for common renaming tasks.
In some specific cases, these default settings might not be appropriate.
A Better Finder Rename shows a thumbnail of the file to be renamed before it asks you to confirm the renaming operation.
Creating thumbnails is usually a quick process of a few hundred milliseconds, but when you deal with very large files the thumbnail creation can take a long time and break the flow of the experience. Some users routinely deal with photo files that are 50Gb and more and obviously creating a thumbnail for such a file on the fly takes a long time.
For these cases, you can switch off thumbnail creation in the preferences:
Preferences...
item in the A Better Finder Rename 12
menuGeneral
tab, un-tick Generate QuickLook thumbnails for confirmation dialog