TL;DR: Next time you want to download the newest stuff in the communityassets git repo, do a full clone instead of trying to pull changes. Otherwise you'll get warnings.
When I created the communityassets repo I was a bit sloppy, and didn't set up LFS. "Git LFS" is a way to separate the management of large binaries from the ordinary version management. It moves the binaries outside the normal github repo (I think onto a separate server), and makes the processing of them more efficient. Without LFS, binary files will be treated as if they're diffable.
Now, however, I have set up LFS and used a brute-force tool (BFG repo cleaner) to convert all large binaries. Unfortunately, this also rewrites the history of the repo, making existing clones incompatible. So if you do a git pull now, you'll get a lot of warnings. Instead you should make a new clone to get the updated repo history.
Apart from this, the change shouldn't really be visible for normal users. The downside of it is that a full clone takes a bit longer, but the upside is that other operations will be faster.
If you're interested in the gritty details, see this https://www.youtube.com/watch?v=uLR1RNqJ1Mw and this https://git-lfs.github.com/