h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

One other reason for using assembly language is that the code takes up less memory than a similar program written in a high-level language and then compiled. I have worked on systems where the memory capacity was measured in kilobytes, not megabytes. Use of assembly language was essential.

An optimising compiler should be able to deliver assembly code that is at least as tight as human coded assembler. Techniques such as loop unrolling which give significant performance gains will tend to be too arduous to do by hand....it's just that a lot of the HLL compilers are very sloppy at optimisation.