Though, a small amount of assembly and a small understanding of processor design and implementation (I highly recommend MIT 6.004) go a long way into having a better mental model of what Java/JavaScript/C/C++ are actually doing under the covers and what's going on.

I was working on a project where I looked at the Philox4x32 random number generator specification and implemented it in Java. A colleague was trying to speed things up by porting it to C++ and so he just used the liberally licensed reference C++ implementation. He couldn't figure out why my Java implementation was significantly faster than the C++. I had a look, at the C++ implementation, and they missed an optimization to save one register in the inner loop. I didn't disassemble the native binary or have the JVM dissassemble JIT'd code, but I guessed that a register spill (32-bit x86 is pretty register starved) in the inner loop was the problem. Just by applying my optimization, he got the C++ implementation faster than the Java implementation.

If we take "this" to mean low-level programming, it can open doors into anywhere from reverse engineering, to OS development etc (or more boringly, writing toolchains). Some parts of compilers rely heavily on having real problem solving skills at this level - for example most books won't teach you how to integrate ELF into your compiler, let alone DWARF.

I am hesitant to say performance optimization because many people have an idea of a CPU just executing one instruction at a time rather than the heavily pipelined and out of order monsters we have today.

To become Anger Fog, you must first invent the CPU-niverse.

(Agner is a almost mythical figure for many compiler and microarchitecture folks)