Styles duplicate when you copy objects with the same styles from different files. The script finds duplicate style names, changes style to first instance, and delete copies.
The plugin fixes the styles names only and don’t change the real properties (don’t synchronize them) so all styles with the same names should have the same properties.
You can “Check for duplicates” or “Remove duplicates”. If you have big amount of elements (layers), script will work extended period of time, so don’t worry if Sketch is “frozen”.
Please backup your .sketch file before use