For me, the former means to protect realistically against >75dB such as cycling on busier roads. Overprotecting, for me, would be using earplugs in quiet environments because I'm anticipating a noise that's a low likelihood of occuring (fire alarm, someone shouting in the office).
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2/ This is entirely dependent on the severity of your T, hyperacusis and/or noxacusis. For instance, 60dB may be your upper limit. I hope someone else chimes in to give you another perspective.