Mostly for speed when working with digital photos/video editing of home movies...basically super-multi tasking. They say you need @ least 512 to run with new and updating windows and I want to keep the notebook for awhile - isn't it smart to spend a little extra $$ and get the 1GB RAM or no?
He might want to bring his laptop with him on trips. He might want to do editing/play games at his hotel room. Desktop, although heavy, still provide benefits over desktops.
If you want to get a desktop replacement, get a turion 64. The only advantages the penium M gives over the turion is better battery life. The turion is better in most apps, and obviously has 64 bit capabilities.