A few practical use cases that are not easily covered by similar platforms:

1) Direction finding thanks to the 8x 153 MSPS ADCs and coherent clocks.

2) Mixed domain analyzer: have one daughterboard act as a RF receiver, and at the same time sample an analogue voltage with the other one. This is a capability reserved to the most expensive of test equipment and lets you analyze how a RF switch is behaving (or do side channel attacks?).

3) Sample almost 600 MHz of bandwidth in real time, use the powerful DSP core to run FFTs on it and send the results over to a browser that implements a RTSA display. This lets you have a real-time view of the spectrum around you for just a few watts. Thanks to the double-PPLs on the Granita board, you can also sweep the spectrum very fast.

4) There is enough processing power onboard to enable RFNM as a 5G RedCap node. We are working with NXP to add an eSIM, so with the right software, this can become a fully-functional 5G UE and connect to the normal cell network. Don't care about 5G? You can write your own standard and deploy it on the same hardware (the limitation here is having access to NXP's DSP development tools, which might limit the processing to the beefy i.MX 8M Plus, but some cores will be available as binaries).

5) Technically, anything requiring an insane amount of ADCs and DACs. You can implement your own board, as the heavy lifting (the motherboard) is already done for you. You could prototype something easily with the development board that's on the website and turn it into a real design within weeks.

Tons of applications and uses in electronic warfare and electronic intelligence gathering.

Also forms a lot of the basis of RADAR, though that's a separate use case.

To oversimplify: SDR allows you to build a radio based around math instead of complex electronics - or, at least fewer complex electronics. It sacrifices a bit of performance but confers a lot of the advantages you get in other software systems - updates, reconfigurability, etc.

Many radio systems are already SDR, just closed. The benefits are the same as building anything into software rather than hardware: you can update it later, support more variations, etc. The downside is more power consumption, so cellphone radios are not usually completely SDR (not an expert on those so correct me if I'm wrong)

This site has some great examples on what various inexpensive SDR hardware can be used for: https://www.rtl-sdr.com/. Use cases range from receiving weather satellite imagery, to reverse engineering radio protocols (e.g. for remote door openers). Several years ago I used an inexpensive DVB USB dongle containing the RTL2832U chip (which enables SDR), to sniff 2G/GSM broadcast packets.

compared to other radio solutions, being able to do more digital analysis on the raw signal lets you do cool things that were previously impossible

at one place, we replaced entire banks of traditional radio scanners using a single SDR

a scanner could only dial into one frequency at a time, but an SDR let us capture entire swathes of the frequency spectrum and extract concurrent streams from multiple sources simultaneously

I'd love to sit down with my Lime and end-to-end my own cell base station... one day