[daeken]

Compiler intrinsics, binary patches and hooks (although EasyHook has made assembly a rarity here outside of the occasional shim where odd calling conventions are used), in-process debuggers, low-level bootloaders, hardware initialization/management, various thunking mechanisms.

Others have covered the optimization side of things well so I won't repeat it, but there are tiny fragments of assembly all over the place -- they hold your system together.