There are a number of reasons to let the airline know. The crew will have the details, so they will be aware that specific accomadation should be made, including, potentially, an individual safety briefing.
I'm not sure about hearing impairments, but visual or mobility disabled passengers and the rest of their booking) can prebook seats (so the carer can be guaranteed to sit with the person concerned) and get preboarded. Both issues are partially for the benefit of the airline , but also reduce the strain of the process on the passenger and their party.
Far from "unnecessary fuss", it's a process that exists for a reason, and benefits both sides. Once onboard, you can always politely advise the cabin crew that you have everything under control.