It seems nonsensical: Why sentence a defendant to more than one “life” sentence? Life is, after all, life.
But there are actually practical reasons why courts impose sentences that exceed “life.” These kinds of sentences frequently arise in murder cases involving multiple victims. (The 2013 punishment for Whitey Bulger is an example.)
In some jurisdictions, a “life” sentence is a misnomer: The defendant may be eligible for parole after a set number of years, like 25. But even where the sentence is life without the possibility of parole, consecutive life sentences may serve a practical purpose.
Suppose, for example, that a defendant is on trial for two murders. The jury convicts him of both, and the judge sentences him to consecutive life sentences. He appeals the convictions and a court overturns one because the prosecution didn’t comply with its discovery obligations. That takes one life sentence off the books—at least until the defendant can be retried. But the other life sentence remains in effect.