Is assembly language useful to learn?

It's a low level programming language for a computer programmable device, it is a very strong correspondence between the language and the architecture's machine code instructions.
Each assembly language depends on computer architecture yes it is important to learn it because otherwise you will not be able to understand the computer language.

practically no :D

As an assembly language developer for years:

I can say DEFINITELY  YES

till the moment there are some parts in software that must be written in assembly language like parts of drivers

also if you want to use some special instruction set provided by the processor , which the compiler know little about for example: Using SIMD instructions to optimize performance

in Intel x86 processors these instructions are named: MMX, SSE1, SSE2,SSE3,SSE4,AVX

and on ARM architecture the latest sets are : NEON, and VFP3