Andrew M. Greenwell writing on Catholic.org from his own experience:
During my confession, I told Fr. Bourgeois that I had been a Catholic, that I was currently attending the Episcopal Church, but that I wanted to confess my sins. Fr. Bourgeois explained that he could not absolve me of my sins unless I agreed to return to Sunday Mass. As a Catholic, I had an obligation to attend Sunday Mass, he explained, and this obligation was not satisfied by the Episcopal liturgy. I told Fr. Bourgeois that I was not ready to agree to such an imposition. So he very kindly but resolutely refused me absolution, and he gave me a blessing instead.
“Receive the Holy Spirit,” were the words of Jesus to his apostles, “If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained.” (John 20:22-23) The power to forgive sins is one of the most precious gifts Jesus left his Church. It is dispensed in the Sacrament of Confession, also referred to as the Sacrament of Penance or the Sacrament of Reconciliation.
The Sacrament of Confession is a great grace. The grace of God’s forgiveness received through the words and hand of a Catholic priest–who, when he acts as alter Christus and in persona Christi (“as another Christ” and “in the person of Christ’) as he does in Confession is as close to the mercy of Jesus as you will ever get to this side of Heaven–is indescribable. St. Thomas Aquinas says that the conversion of a soul is worth more than the entire universe. The Sacrament of Confession participates in that supernatural gift of infinite value, God’s mercy and sanctifying grace.
Priests are taught to be generous in meting out God’s mercy through this great Sacrament of Reconciliation. They are to err in giving absolution. The salvation of souls is the supreme law. But there are times where this great gift must be withheld, where absolution must be deferred or refused outright, and where it would be great error in dispensing it.
Unquestionably, there is great grace in receiving absolution, but is there grace in being refused absolution by a priest in the Sacrament of Confession? The answer (I speak from experience) is yes.
To read his detailed explanation, please click Here.
Catholicism Pure & Simple 
One may get confused by examples of freefloating believers e.g. attending Catholic Communion when Episcopalian! You suppose them to be utterly sincere…it helps if you don’t use newchurchspeak and call it the “shared meal”.
By accident, when I was a guest chorister, I received the Body & Blood of Christ in an Anglican Cathedral- later it was (Somewhat Forcefully) explained to me that however much you may love your fellow Anglicans, you don’t eat with them (metaphorically speaking- since they are merely “metaphorically speaking”).
Existentially speaking, I did feel I had received the real inspiration of Christ’s presence: it was a precious and holy experience (was it “technically” transubstantiation…am too theologically challenged to say!!) Having rather laboriously worked out that- as in mathematics- Anglican belief was a subset of Catholic belief (as in ‘diluted’) I had supposed that the sin would be to attempt communion in the fuller faith when not sincerely convinced of it, and one was answerable to a greater responsibility according to the degree of faith required (not that you could treat a Quaker Meeting like a picnic…)
A few years later, the Anglican Dean who presided, chose to be accepted, with his congregation, into the Ordinariate.
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