For the same reasons any 64-bit application is desirable, to be able to address more than 4G of VM. Although in this case it's not a particular app but the JVM for Java apps so in theory a64-bit ...

IBM plans to make 64-bit Java technology available on its AIX 5L Unix operating system in early July, a move that it claims puts AIX ahead of Sun's Solaris and Hewlett-Packard's HP-UX operating ...