From some research I’ve done (such as this article:
catholicexchange.com/parish-registration/ ) parish registration is purely a matter of convenience and has no definitive basis in canon law. It is not a matter of necessity; America has particularly given it higher importance than it actually has. The Church’s diocesan jurisdiction is based on territory, not on registration. One can register in a distant parish, but one’s home parish is based on the territory in which they live. This itself is only truly significant when it comes to marriages (where a marriage in a foreign territory is invalid unless approved of by the priest of one’s home parish). As the article says, “The law does not require anyone living within the parish boundaries to take the additional step of registering at the parish. The very fact that a Catholic lives in the territory of a particular parish is enough to make him a member… These canons that refer to a person’s parish always refer to the territorial parish of the Catholic person. Whether that person is registered at a completely different parish, or is not registered anywhere at all, is canonically irrelevant.” Also: “The fact that a person has or has not registered in a particular parish can never be used in a way that would directly violate canon law.”
I believe, in my opinion, that this should also apply to the familial life of the parish - such as accepting prayer requests. Simply by living in this territory, I am a member of my parish, regardless of whether or not I have registered, and for my parish to completely exclude me from submitting a prayer request (for a young Catholic girl with leukemia who died from it only a few days later) or from joining a prayer group is, I believe, wrong.
However, I have also found a possible reason why registration, especially in America, is given such high importance: tax deductions. One of the main functions of being registered is to receive donation envelopes which, at the end of the year, are tallied and the individual is given a sort of receipt detailing the amount of their tax-deductible donation. I do not mean to judge anyone, but if this is the or even a reason why registration is so significant here, I think this is a serious moral issue. I am against the very idea of tax-deductible donations, and especially for Church donations, as a tax deduction gives a reward to something that should be a completely free gift without payment. This is my belief.
Now, just to clarify, I am a faithful Roman Catholic. I love the Church and respect all Her teachings, including those about diocesan and parish jurisdiction as explained in Canon Law. It is precisely because of this love of the Church that I try to point out what I view as an abuse by Church members, something that can be a stumbling block for believers and non-believers alike. I am not trying to sow dissent in any way. God bless.