Try riding with ear plugs, on a busy road - you will soon get the idea.
Yes a stupid question. Obviously, having heard an approaching vehicle, you will want to know from which direction it is coming and will have a look around, if you can't already see it.I have another question (which you will no doubt consider stupid): If you cannot (as you say and I agree) determine where a vehicle is from the sound, are you not better off just looking (in which case the sound is irrelevant)?
The point is - if your hearing is impaired you may not hear it, as well as not seeing it.
In point of fact good hearing is also directional - you get a good idea about the direction of the source, naturally. The ears are cleverer than they look.
When your hearing goes, even with hearing aids, this directionality is lost.