When should a patient be offered palliative care?

When risks > benefit: No black and white answers here, but when the risks / complications / side effects of treatments begin to outweigh the benefits then it's time to think about quality, not quantitiy. In a perfect world the patient/family could accurately add up all the positives and negatives in a numerical fashion and make their choice, in the real world it takes a long / honest /open two-way discussion.

When is no cure: Palliative care is provided for somebody who has a life-threatening disease for which there is no cure and that may cause death but it is not clear when.

For comfort. : Palliative care should be offered when a patient is having significant symptoms from a terminal or incurable medical issue. It involves controlling the symptoms rather than treating the actual condition.