Although 32-bit programs will run in a 64-bit environment, 32-bit DRIVERS will not! This has caused endless problems for those of us with devices, such as camcorders, using firewire to connect to the pc - the IEEE 1364 driver was updated to 64-bit but many of the camera manufacturers did not provide 64-bit device drivers for their (legacy) hardware.
So, one reason to create a dual boot to 32-bit XP would be to access such hardware. If all you want to do is run old 32-bit programs then it is probably not worth it - unless those programs, such as some games, directly access some hardware (often the monitor) through drivers rather than through windows.