[SAI_Peregrinus]

RPis (and similar) are interesting because they're a tiny full-fat Linux computer with user-accessible GPIOs. That's the only special thing about them. There are other tiny Linux computers, but RPi-like computers have GPIOs, so they can use communication protocols that don't have standard external headers like I2C & SPI, switch relays, etc. They're interesting precisely because they can do what a microcontroller can do, while still being a full Linux system.

I mostly use them for situations where I'd otherwise need a small Linux computer and a microcontroller together, e.g. for CAN + DoIP simulation with SCPI control of test equipment over Ethernet & relay control of a vibration table.