Some time ago I bought 320GB hard disk to my desktop machine (which also is my main developer box). I decided to try LVM on it and created one volume group which consists whole HDD. There is one partition on it: /home. It works good but I still had 104GB not used on older disk.
Today I finally found time to extend LVM to get use of old hdd space. Few commands later I have 400GB /home partition which use two discs and is easy to expand in future.
But desktop has easy configuration. When I bought Dell D400 I decided to remove Microsoft Windows XP from it (legal copy) and use this machine only under Linux.
Booted Debian ‘Etch’ installer via PXE/TFTP and split hdd into two parts: /boot partition and rest for crypted LVM. During start I am asked for passphrase and then rootfs is mounted, machine is booted into KDE. Swap partition is also crypted so even after suspend you can not check what was running.
So LVM is good solution if you have few hard disks in machine and does not want to think how to mount them to have them best used — simply join them into one big partition and mount (or few partitions but with easy resizing). It is also good when you want to crypt data — easy to configure and setup. The only minus is that it require initramfs if you have rootfs on LVM. But Debian makes this thing also easy to do :)