When it should be a space instead. There’s a distressing trend we’re seeing in sentences that have two verbs but are not compound sentences. Writers these days are often prone to stick in a comma before the conjunction preceding second verb, where it does not belong.
Why? Typically because the sentence in question is getting long, and the writer believes a pause is called for. Grammatically it is not. But that misplaced comma is a good signal to take a second look at that long sentence. Perhaps it can stand as is. Perhaps that stray comma has changed the intended meaning entirely. Or perhaps it should be broken into two sentences to make the text more readable.