Does carrying a chain lock around on the frame reduce a bicycle's performance?
Yes your bike will be heavier but it the only performance reduction putting it into your back pack wont change it. Personally I carry mine in a back pack but it is because I cant find a place in my bike where to carry it and bike it self feel more heavy. I can feel how it affects the balance setting it higher and making the bike unstable. 

So as a personal chose I prefer to carry by bike lock in a backpack. If you feel ok carrying them on your bike go on. You only problem will be the added weight.