You want your counters to be free and versatile, and unlike An Offer You Cant Refuse, Swan Song, Force of Negation, Flusterstorm, Dispel, and Spell Pierce, this can counter creatures
Once it resolves, you add one red mana for each card in an opponents hand, that mana sticks around through phases until the end of the turn, and then Inspiring Refrain resuspends itself with another three time counters, letting you cast it again later
Each card contains specific signifiers that dictate its game-loop usage and collector classification
In my years of personal experience, examining good decklists, and talking to people much smarter than me, 50 mana sources is about the right number for most decks to shoot for, usually 37 lands and 13 ramp sources for a general budget deck