  Prepare-and-measure scenarios, in their many forms, can be seen as the basic
building blocks of communication tasks. As such, they can be used to analyze a
diversity of classical and quantum protocols -- of which dense coding and
random access codes are key examples -- in a unified manner. In particular, the
use of entanglement as a resource in prepare-and-measure scenarios have only
recently started to be systematically investigated, and many crucial questions
remain open. In this work, we explore such scenarios and provide answers to
some seminal questions. More specifically, we show that, in scenarios where
entanglement is a free resource, quantum messages are equivalent to classical
ones with twice the capacity. We also prove that, in such scenarios, it is
always advantageous for the parties to share entangled states of dimension
greater than the transmitted message. Finally, we show that unsteerable states
cannot provide advantages in classical communication tasks, thus proving that
not all entangled states are useful resources in these scenarios.
