With 3 to 5 tones the ear can quickly and easily match a specific pitch to a specific RANGE of conductivity. That doesn't mean the goal of 50 tones is trying to memorize dozens of conductivity/pitch pairs. Instead, it's a different way of listening. The general relationships between conductivity and pitch are still important, such as low, medium and high, and there will be specific tones you eventually internalize with enough experience using the same settings, but the point of more audio information is to hear more audio characteristics. Ascending, descending, stable,narrow, round, long, tight versus loose edges, gaps/separation, etc... You don't have to memorize dozens of conductivity/pitch pairs to get started do that right away.
Not only would trying to internalize all of those pitches be frustrating, we all know that targets vary with any detector, and the skill won't transfer to other detectors, or even the same detector with different audio settings. But, the skill that is transferable to other detectors with more tones is the ability to assess signal characteristics based on RELATIVE changes in conductivity.
The Equinox has options to make make 50 tones easier on the ear, or more complex. See page 48 of the manual. I've never seen anyone mention these setting. They're a million times easier to demonstrate rather than describe in words. All I can say is grab some targets and experiment. Fortunately, you can hear the difference in tones as you adjust the parameters. In short, adjusting the high limit of ferrous in combination with maximizing the gap between ferrous and non-ferrous can make 50 tones easier on the ears. (These features are similar to the Variability and Limit features on the Explorer and E-trac.)
As somebody mentioned above, using 50 tones is pretty pointless if the ground is clean. But, if it's really trashy, the additional audio in 50 tones can help identify separation, pinpoint the conductive center of a target, ID rusty nails, etc...