with assembler you may reduce size of the code, increase speed, use tricks to prevent disassembling or debugging.
of course it does not mean that any program written in assembly is lighter and faster than written in hll. instead, modern optimising compilers may create efficient code more easy, than regular human, especially for large applications.
in any case it's not bad to know how it all works in real
btw, there were a lot of holywar topics about this question already, maybe some of them are still available