Why you should care about the ISA
As developers, you may not need to write directly in assembler in our day-to-day role. However, assembler is still important in some areas, such as the first stage boot software or some low-level kernel activities.
Even if you are not writing assembly code directly, understanding what the instruction set can do, and how the compiler makes use of those instructions, can help you to write more efficient code. It can also help you to understand the output of the compiler. This can be useful when debugging.