Assembly is besides nand or nor gates the closest you get to the machine usually.
To me it depends on what you want to do.
it's a load of mnemonics that are CPU architecture specific that can give you a lot of information.
If you got time and you want to understand it a bit more it can be usefull but if you got time I would rather recommend nand2tetris.org/course
because they take you through everything :) in a strucutred way. including assembly but the approach is wholeistic :)