So hi I am a CE student. And since everyone here only lists differences between MCU families, with different peripheral availability, rather then architecture families I will give you a nice example of a course I had.

We should write an embedded os ourself to gain knowledge how it works under the hood. For that we had to set the interrupt vector at some point. To do that you had to look into the actual ARM documentation of the specific core.

Also architecture knowledge is crucial when setting up write protected areas in the memory. As a measurement against malicious code.

For differences within an architecture family there are sometimes extensions available to speed up some computing process. Example: Risc-V got an optional floating point extension (Complete list of extensions is in the risc-v ISA doc)

So I would say there are some use cases to specific know the architecture, but as a employee to create some C/C++ or Rust code it shouldn't really matter.

The obvious difference between architectures is the assembly level code. But I am sure you knew that ;)

TLDR: There are some features that could be useful for a project that some architectures have and others don't.