Unlike in previous Fallouts, in Fallout 4 limb injuries are instantly healed when the player sleeps, uses Stimpaks, or visits a doctor. This pretty much eliminates limb health as a significant game mechanic. Insult To Injury reimplements this mechanic, taking over limb injury/health and overriding magical limb healing wherever it can.

With ITI, naps don’t magically heal broken bones. Different bandages and splints do different things and with different efficacies. Disease and infection happens (in conjunction with the Bethesda Survival mode disease system). Limb recovery occurs much more slowly, requiring both medical care, plenty of rest, and time.