There’s a configurable cap on max file size to auto-add, IIRC. It defaults to something “reasonable”.
If you do somehow add a terabyte of small files by accident, it’s still just git under the hood so you can make sure nothing active points at them and GC them.
Yeah they usually are, I'm sure it's great because I add files more often than I ignore, but I need to be careful with the temporary files I write left and right in the repo dir during development.
If you check `jj status` regularly and/or use `jj split` to build up your commits (like `git add -p`) then you’ll notice. They might end up in your local repo (until a gc) at worst.