A Raspberry Pi a fairly tiny computer that can run a "real" OS, and that has a fair amount of GPIO that can be bought new somewhat-inexpensively. It has storage that is easily-removed and swapped (whether for good, or for bad).
If all a person needs or wants is a fairly tiny computer and it doesn't need to be new/shiny, then there's off-lease corpo boxes that are faster/better/cheaper.
If all a person needs or wants is some GPIO to hack on hardware with, and doesn't want a real OS on the back end of things, then maybe an Arduino or ESP32 or RP2040 or something might be better and cheaper.
But if a person needs or wants all of that in one box, then: A Raspberry Pi may well be the right approach. (Some folks like hacking with a real OS; this is fine. We used to use things like parallel ports for this in the PC space but those are long gone.)
Or: If a person needs or wants a well-tuned system that they can just download and use specialized images for and write to a MicroSD card, then: A Raspberry Pi can become desirable.
---
For instance: I use a Pi 4 to play movies with over SMB. I could do that a thousand or more different ways, but using LibreElec on a Pi 4 is the easiest way for me to get there -- just download it, stuff it into an SD card, and boot it up. It becomes an appliance, and this appliance is similar or identical to many other appliances; this makes supporting it easy. (And if I want to do something different with that hardware today, it takes only a few seconds to swap its storage for something completely different -- and swap it back later.)
Or: 3D printing. I can do what many others have done before me and sneaker-net gcode from the PC to the printer, or I can use a Raspberry Pi and a standardized Octoprint image to put that printer on the network instead. Now my printer is a network appliance.
If all a person needs or wants is a fairly tiny computer and it doesn't need to be new/shiny, then there's off-lease corpo boxes that are faster/better/cheaper.
If all a person needs or wants is some GPIO to hack on hardware with, and doesn't want a real OS on the back end of things, then maybe an Arduino or ESP32 or RP2040 or something might be better and cheaper.
But if a person needs or wants all of that in one box, then: A Raspberry Pi may well be the right approach. (Some folks like hacking with a real OS; this is fine. We used to use things like parallel ports for this in the PC space but those are long gone.)
Or: If a person needs or wants a well-tuned system that they can just download and use specialized images for and write to a MicroSD card, then: A Raspberry Pi can become desirable.
---
For instance: I use a Pi 4 to play movies with over SMB. I could do that a thousand or more different ways, but using LibreElec on a Pi 4 is the easiest way for me to get there -- just download it, stuff it into an SD card, and boot it up. It becomes an appliance, and this appliance is similar or identical to many other appliances; this makes supporting it easy. (And if I want to do something different with that hardware today, it takes only a few seconds to swap its storage for something completely different -- and swap it back later.)
Or: 3D printing. I can do what many others have done before me and sneaker-net gcode from the PC to the printer, or I can use a Raspberry Pi and a standardized Octoprint image to put that printer on the network instead. Now my printer is a network appliance.