This is an excellent topic and one that doesn't have a clear-cut answer as far as I know. Sometimes I want to have insurance, and other times I'm willing to chance it.
For example, in my PPR league I have McFadden and Matthews. I have Mike Goodson, but I don't have Battle.
The difficulty is that handcuffs, while serving as much-needed injury insurance, also suck up important roster space, and leaves an owner inflexible during bye weeks.
If someone drops their handcuff to pick up a replacement defense, then there's the chance that another owner will pickup the handcuff and then use that handcuff the next week in multi-player trades.
Other times, you drop the handcuff and are fortunate to pick him back up the next week.
I know what you mean. I have Rice and Mathews and carried around Battle for a bit just in case, but not Bernard Peirce. I dropped Battle during byes, but will probably pick him up again after. Certain RBs like Mathews, McFadden, Gore, Bradshaw, etc, seem more volatile than others, and I suppose buying insurance for them is (sometimes) worth the roster spot. But I agree that too much insurance easts up your bench space real quick.
Another way I like to look at it, is if I have a stud RB post-byes, having a quality handcuff on the bench essentially guarantees continuous production from that RB slot, even if the #1 goes down. Thus, if they do go down, you needn't rely on WW priorities/competition or lesser RBs like Brown, Green, or even SJax. In that situation, I find the latter make for great trade fodder.