Drug smuggling. If you don't need to be covert then you could just use active radar, right?
Others have linked the code and an article about someone trying it out. What you can do with this is that you wave around two yagi antenna. You point one at a broadcast source and an other at something flying in the opposite direction from the broadcast source. If all the stars align and the system works you then get the range, and the dopler. The measured range is the full distance from the broadcast source to the object and back to you.
This is not a radar where the user gets a display full of tracks in front of them. One maybe one day might develop something like that from this core.
Even if it were a stealth radar like that it is very dubious how it would help a drug smuggling operation, or why they would bother with it at all.
This is one interpretation, but it's actually pretty reliable.
> This is not a radar where the user gets a display full of tracks in front of them
You actually do get a full radar plot.
See the video at the bottom of https://www.rtl-sdr.com/krakensdr-field-reports-and-software... for a complete tracking of a weather balloon.
Passive radars can be used to track emissions sources of which you have no specific knowledge e.g. you're looking for a ship or rig, but you either don't want to ping it, or you are looking for its rough location, or you literally don't have the hardware for an active radar at the range involved.