initramfs

IMO initrd/initramfs is a great thing for portable operating systems such as live CDs and installers, because there is no way they can know in advance what hardware they might need to support before they are booted. And having an emergency kernel and rootfs populated with recovery tools could easily come in handy.

On regular, fairly static systems, where you don't replace your MBR with a GPT or a BSD disklabel after every other reboot, you can compile the stuff you always need into the kernel image and load additional modules lazily. But if disks and video cards vary from boot to boot, initramfs might actually be considered an optimization, allowing you to disable module unloading and use userspace tools to aid boot.

But none of this is why mainstream distros use initramfs. The actual reason is that they insist on distributing kernel binaries, but are OK with users assembling initramfs images. And who can blame them, compiling kernels takes CPU time.