Asm is simple enough that "mental execution" is far easier, if more tedious, than in HLLs, especially those with lots of hidden side-effects. The concept of a function doesn't really exist (and this is even more true when working with RISCs that don't have implicit stack management instructions), and although there are instructions that make it more convenient to do HLL-style call and return, it's just as easy to write a "function" that returns to its caller's caller (or further), switches to a different task or thread, etc. If you're going to learn Asm, then IMHO you should try to exploit this freedom in control flow and leverage the rest of the machine's ability, since merely being a human compiler is not particularly enlightening nor useful.