Yes, if only for the player to acclimate to the guitar; but I believe an acoustic guitar's tone does change over time. All of mine became deeper (without losing high end) and more responsive after a year or so. I would think these are the qualities "opening up" refers to, though I don't really know what others mean by it.
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Collings OM-2H with cutaway
Cordoba GK Pro Negra flamenco
National Resonator Collegian
Taylor 562ce 12-string
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