What is the current state of the law on mercy in sentencing cases?

In modern Eighth Amendment jurisprudence, mercy is "one of the most central sentencing considerations, the one most likely to tilt the decision in favor of life." (Drake v. Kemp (11th Cir.1985) 762 F.2d 1449, 1460 (en banc).) "Just as retribution is an appropriate justification for imposing a capital sentence, [citation], a jury may opt for mercy and impose life imprisonment at will. The ultimate power of the jury to impose life, no matter how egregious the crime or dangerous the defendant, is a tribute to the system's recognition of mercy as an acceptable sentencing rationale." (Ibid.)