the immaculate conception is a product of the monastic movement after emperor Constantine legalized Christianity as a religion (although he himself really nothing to with the development itself).
The basic concept is Mary was born without original sin, and never sinned in her life, at least up to the birth of Christ, the Son of the living God. The significance of this later tradition was initially was to highlight how holy Jesus is. (After all, how can just anyone be worthy to bear God incarnate?) And as time drags on and what the logical conclusions demand of the immaculate conception resulted the elevation of Mary herself. Which further escalated the Marian modal of sexual purity, observance, hyperdulia, Mary's ascension; even more insane marian concepts like Ark of the New Covenant, the new Eve, and the Catholic doctrine of Marian mediatrix.
How influencial is this version of Mary in catholic? If you, as a Catholic, for any reason wasn't aligned with God and cannot contact a priest, then (according to Cathology) you can do the hail mary prayer 10 times and you'll be temporarily theology safe.
At this point, honestly we shouldn't be too surprised if the Vatican II declare Mary as the incarnation of Sophia in Psalm 50.