My list (the list may have items on it for which there are "Perl" modules doing the thing mentioned, but typically such modules contain large parts of C and/or XS code - which isn't Perl).
Number crunching. Accessing the value of a number requires following at least two pointers, plus some additional overhead to check to see whether the numeric value is correct.
Anything that requires to be CPU/register/memory/cache friendly. The flexibility of Perl comes with a price, and that's paid with CPU and memory.
Anything that requires a small footprint in disk space. Compiling C programs with the right compiler can give you programs of just a few k, meaning you can pack a lot of them on a floppy. There's no way to install perl on a floppy.
Direct memory access, due to the lack of pointers.
Locking regions of files instead of the entire file.
Calling kernel hooks.
Many things for which there are special purpose languages (music, vector images, etc)