Well, mostly by the time you have a corrupt ODM, you either no longer have a system, or you have a system which doesn't function properly.
In most cases you'll be in contact with an IBM support organization, and if any ODM corruption is suspected, it is always handy to be able to provide a recently made backup of the ODM files.
And yes, a recent mksysb tape or cd can prove unvaluable!
HTH,
p5wizard