This field allows you to set a numeric limit to how many unique tag names your local repository can hold. This field uses FIFO (first in, first out) logic meaning that once you upload a new unique tag name that exceeds the set limit, your oldest tag will be removed and your new unique tag will be stored instead.
By default this field is set to zero (0), meaning that there is no limit and you may upload as many unique tag names as you like.
Example of Max Unique Tags Usage
In your repository, you have three unique image tag names that were pushed to your repository in this order: V 1.0.0, V 1.0.1, and V 2.0.0 (V 1.0.0 being the first, and V 2.0.0 the last).
In this repository, Max Unique Tags is set to 3, meaning that at any given time, you can only store 3 unique tag names: V 1.0.0, V 1.0.1, and V 2.0.0.
In the diagrams, the green boxes = stored tags, and the gray boxes = deleted tags.
Next, you upload an additional tag: V 2.0.1. Because V 2.0.1 has a new and unique tag name, it will exceed the Max Unique Tags limit that you have set on your repository, and therefore your oldest tag, which is V 1.0.0, will be removed to make space for the new V 2.0.1.
The result would show that your repository now stores V 1.0.1, V 2.0.0, and V 2.0.1.
If your artifactory instance has Trash Can enabled, you will be able to retrieve removed tags if needed.