really depends. since he wants to run linux off a usb, then it won't really need a true dual boot menu. boot order is good enough. set the usb drive as first in boot order. then if it is there, it will boot to linux first. if the usb is not there, then it will move to second on the list which is the hdd and it boots to windows.
if it was all on hdd's then yes a multi-boot menu is desired (though not 100% needed) so you can chose as you go. if each OS is on a separate drive, then calling up the boot menu at start-up can be used to select between Os's as well.
so dual boot menu is useful, it is not mandatory really. running mac os as a hackintosh is the exception. boot camp is needed to run windows as well as mac os on the same pc as...