How to use Sourcetree + Azure DevOps + Git LFS?

I've managed to successfully clone a couple Azure DevOps repositories using Sourcetree, but I'd like to make sure I'm using Git LFS with them so that I'm properly managing binary files.

I found the Git LFS menu in Sourcetree under Repository > Git LFS, and I selected Initialise Repository. I'm using this workflow to develop for Unreal Engine, so I added two types of files to track to start: *.umap and *.uasset.

To be clear, I didn't know Git LFS wasn't setup by default, so I initialized the repository after I had received a warning that one of my *.umap files was over 10 mb in size. Once I initialized Git LFS and started tracking the specified file types, I noticed that the *.umap file was staged with both a + and - sign, which is different than how it usually looks when committing.

Does this indicate that it's working properly? I'm new to managing non-code related files using Git, and from what I've read, Git LFS seems like a powerful way to manage large files, so any help understanding this would be helpful.

Thanks!