The whole point is to make filesystem layouts less dependent on the hardware limitations. you can partition a disk for a filesystem, but with lvm, you can combine disks into larger containers for filesystems. There's more, but I recommend the lvm pages at the linux documentation project:
www.tldp.org. they are very useful to explain what and why. AND it keeps me from accidentally telling you incorrect information!
I expect that wikipedia has several articles as well.
--jason
