uv uses some very neat tricks involving hard links such that if you start a new uv-managed virtual environment and install packages into it that you've used previously, the packages are symlinked in. This means the new environment becomes usable almost instantly and you don't end up wasting filesystem space on a bunch of duplicate files.
This means it's no longer expensive to have dozens, hundreds or even thousands of environments on a machine. This is fantastic for people like myself who work on a lot of different projects at once.
Then you can use "uv run" to run Python code in a brand new temporary environment that get created on-demand within ms of you launching it.
I wrote a Bash script the other day that lets me do this in any Python project directory that includes a setup.py or pyproject.toml file:
uv-test -p 3.11
Which means I can test any code I like against different Python versions without any extra steps.