At a guess, those applications routinely require large amounts of mostly random (not CSPRNG random) numbers. This syscall returns data from the kernel's entropy

At a guess, those applications routinely require large amounts of mostly random (not CSPRNG random) numbers. This syscall returns data from the kernel's entropy pool, presumably at the speed of /dev/urandom. The recommendation is probably a way to say "please don't abuse, and please don't make the kernel spin".