Why Would You Go For Lighter Weight...
...in a home-defense gun?
If you envision scenarios where five rounds would likely suffice, it can be argued that the shorter barrel (less than 2 1/2") makes it harder for an assailant to wrest the revolver from your hand. However, if you are impressed with that argument, why not go with a stainless-steel Centennial, at greater weight? The greater weight will dampen the recoil more effectively, making it much more likely that you will have productive training sessions. Additionally, the lighter the weight of the gun, the more likely it is that you will divert the muzzle from your point of aim when you apply a few times the weight of the gun in pressure to accomplish the double-action trigger stroke.
While there are arguments for the lighter guns for concealed carry, if I have the opportunity to slip a third Centennial into my pants pocket (in addition to the two 640-1's on the belt), it will be the stainless-steel first-generation 640, not the 442 or 642. While I may shoot the latter guns okay in a casual range session, I know that I will be able to handle the slightly heavier gun better under stress.
As has already been suggested, a larger revolver, with at least a six-round capacity, may be a better choice for home defense unless that size gun is too large for you to fire reliably.