Well, it likely depends on your machine, the environment your hunting in as well as experience.
However, through my first 50 hours of (beach) metal detecting I have the results of being both Sensitive (dig everything) and being Specific (dig only mid and hi tones). Remember that these are not US coins and most of them give me a mid-lo mixed signal and indicated as a pulltab. Essentially there is no statistical difference if looking at the time spent & coins found.
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Overview of my metal detecting hobby.
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Sensitive (Dig All)
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Values
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[TD="align: left"]Hours Spent[/TD]
[TD="align: right"]27.75[/TD]
[TD="align: left"]Value Found[/TD]
[TD="align: right"]R$ 18.94[/TD]
[TD="align: left"]Value/Hour[/TD]
[TD="align: right"]R$ 0.68[/TD]
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Counts
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[TD="align: left"]Junk[/TD]
[TD="align: right"]822[/TD]
[TD="align: left"]Coins[/TD]
[TD="align: right"]48[/TD]
[TD="align: left"]Jewelry[/TD]
[TD="align: right"]0[/TD]
[TD="align: left"]Relics[/TD]
[TD="align: right"]0[/TD]
[TD="align: left"]Targets[/TD]
[TD="align: right"]870[/TD]
[TD="align: left"]Targets/Hour[/TD]
[TD="align: right"]31.35[/TD]
[TD="align: left"]Coins/Hour[/TD]
[TD="align: right"]1.73[/TD]
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Specific (Hi-Mid tones Only)
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Values
[/TD]
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[TD="align: left"]Hours Spent[/TD]
[TD="align: right"]22.00[/TD]
[TD="align: left"]Value Found[/TD]
[TD="align: right"]R$ 12.64[/TD]
[TD="align: left"]Value/Hour[/TD]
[TD="align: right"]R$ 0.57[/TD]
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Counts
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[TD="align: left"]Junk[/TD]
[TD="align: right"]392[/TD]
[TD="align: left"]Coins[/TD]
[TD="align: right"]27[/TD]
[TD="align: left"]Jewelry[/TD]
[TD="align: right"]0[/TD]
[TD="align: left"]Relics[/TD]
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[TD="align: left"]Targets[/TD]
[TD="align: right"]419[/TD]
[TD="align: left"]Targets/Hour[/TD]
[TD="align: right"]19.05[/TD]
[TD="align: left"]Coins/Hour[/TD]
[TD="align: right"]1.23[/TD]
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Total
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Values
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[TD="align: left"]Hours Spent[/TD]
[TD="align: right"]49.75[/TD]
[TD="align: left"]Value Found[/TD]
[TD="align: right"]R$ 31.58[/TD]
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Counts
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[TD="align: left"]Total Junk[/TD]
[TD="align: right"]1325.00[/TD]
[TD="align: left"]Total Coins[/TD]
[TD="align: right"]77.00[/TD]
[TD="align: left"]Total Jewelry[/TD]
[TD="align: right"]0.00[/TD]
[TD="align: left"]Total Relics[/TD]
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[TD="align: left"]Total Targets[/TD]
[TD="align: right"]1402[/TD]
[TD="align: left"]Targets/Hour[/TD]
[TD="align: right"]25.15[/TD]
[TD="align: left"]Coins/Hour[/TD]
[TD="align: right"]1.38[/TD]
[TD="align: left"]P-value (S vs. E)[/TD]
[TD="align: right"]0.0691435242[/TD]