Allowing it to cool below the phase transition point of the melted plastic will cause it to release latent heat, so there is a theoretically possible corner cas

Allowing it to cool below the phase transition point of the melted plastic will cause it to release latent heat, so there is a theoretically possible corner case where maintaining it hot saves energy. I suspect that you are unlikely to hit this corner case, though I am too lazy to crunch the numbers in this comment.