An auto merge feature in Duplicates is available to help to reduce the amount of time spent assigning items to merge. This can be switched on from Settings > Configuration > Duplicates Settings
The auto merge feature will merge matches that have been given the confidence score of 13 or above and are single matches (i.e these are duplicates that would appear on the single matches page).
The confidence scores are detailed within the article Duplicates - Overview
|Key info: If you want to preserve duplicate constituent profiles that would be automatically merged then this option should not be enabled.|