Bats and Whales, and some monsters like the Hook Horror, have blindsight based on hearing. You can tell it's based on hearing because they also have the Echolocation trait that says their blindsight does not work if they are deafened. For the purpose of this discussion, please assume a totally dark environment.
Beyond the range of their blindsight, these creatures can use their mundane hearing to detect other creatures, and they can benefit from Keen Hearing, giving them advantage on Perception checks that rely on hearing. Within range of their blindsight, what changes? Do they still benefit from Keen Hearing? And how does blindsight change what they can perceive over and above mundane hearing?
In particular, to what extent can they pinpoint the exact position of creatures within and outside the range of their blindsight?