I have seen this a couple of times before in published works. In my fields, it does not occur too often.
Uncited references refer to relevant papers, books etc related in some way to the study in the paper, but were not directly cited in the study itself (they are included in the References section). Essentially, it is an 'additional reading list'.
This can potentially add some legitimacy to the study by listing related published peer review research, but also could be seen as unnecessary 'clutter'.