Sequential circuits and memory
"Sequential circuits" is an abstract idea. A Set-Reset latch made of cross-coupled NOR is just one example of a way to realize a sequential circuit. Could also be built from vacuum tubes or op-amps (with positive feedback and hysteresis) or some types of mechanical relays or even mechanical cogs and gears. Same basic design principles apply to all sequential circuits, regardless of the underlying technology. Technology changes. You're not studying a technology, you're studying the underlying design principles.

Arithmetic operations (such as unsigned 2's complement addition and subtraction) can be made from Combinational circuits (gates). Putting combinational circuits together with sequential circuits makes finite state machines, which lead to more complex machines like computers.

Abstract ideas are powerful but can be hard to grasp without a specific example, that's why your coursework is focusing on SR latch as a specific example of a simple sequential circuit element. It's something you could reasonably test in the lab and it's pretty close to what you will likely see in practice.


Side note: yes, at one point in history computers were built out of relays. Sometimes debugging required scooping out an actual insect: https://www.computerworld.com/article/2515435/moth-in-the-machine--debugging-the-origins-of--bug-.html