1) I know I'll be doing something different, and I don't know how much disk to allocation to Partition N for Program X. LVM allows me to leave unpartitioned space on the drive, and dynamically allocate it as needed. (Note that this is a fairly mild benefit, save in corner cases.)
The benefit is not so mild when you add a new disk to your system -- you can add it to the group and expand a partition beyond the single disk.
This is *not* generally recommended because now a single drive failure will bring down two disks worth of data, but is handy for a temporary situation.
Bryan