Content limitations, in the context of Normal Waking Consciousness, refers to the fact that we tend to "limit" the content of our thoughts and feelings when we are alert and awake in normal waking consciousness. This is because our alertness in this state makes us more vulnerable to feeling hurt or embarrassed or depressed if we, for example, think about something humiliating that happened to us or think about something that caused us grief.
By having content limitations in NWC, we protect ourselves from being exposed to such potentially hurtful thoughts or remembrances. On the other hand, content limitations become lowered or even non existent in Altered states of consciousness, such as sleep. For example, we might have a dream about something traumatic that happened to us, and we can't control whether or not we are reminded of that experience because content limitations cannot be applied in altered states of consciousness as well as they can be in NWC