Feature is for Sales managers to be able to coach their reps to excel performance. Aircall & Salesloft both have this tool and it allows them to shadow calls, listen in and whisper.
This, along with a plethora of other SEP functionality, is tablestakes these days.
Please get with the times, HubSpot team!!!
I need this feature. Seems really out-dated that a company like Hubspot cannot support this without a 3rd party integration.