For centuries, Roman Catholics belonged to territorial parishes. That is, wherever they lived determined which parish they attended, and they also had obligations to support the material needs of this home parish, and their home pastor had a significant influence on whether these folks could marry or pursue a vocation to the priesthood or religious life. Of course, any family with children would send them to the parochial school where they belonged (there were often regulations that prevented the kids from going anywhere else.)

However, the popularity of cars, highways, and general mobility all over the place, has caused many bishops, particularly in the United States, to sort of supersede these territorial rules. Now in my diocese, a Catholic can go attend any parish they want to, and register in that parish, and for all legal purposes they are an official member of that parish, as if they lived within the territory. There have always been parishes like this, called "personal parishes" but they were often defined by certain ethnolinguistic qualities, like everyone from Poland, or Vietnam or something.

So now this leads to some crazy situations. For example, my friend was received into the Church from Lutheranism, and when this happened, he lived in a particular place. But he's moved away--far, far away--twice, and yet he still "commutes" to that parish where he became attached and still loves, and still has commitments and responsibilities there, which he upholds.

There are also people who, for liturgical or doctrinal reasons, will drive for hours on Sundays just to reach a church that agrees with their personal beliefs and preferences.

I am not sure this is sustainable or realistic. If eventually you have Catholics driving all over creation, literally, to get to their preferred parish, then some parishes are going to languish, if they cannot attract or retain people who are willing to volunteer there, support their material needs, and send their kids to the parochial school. That means schools are going to close. There are also independent schools popping up, that are not parochial, but approved, and Catholics send their kids there. Failing that, they get homeschooled.

I think this extreme mobility thing is absurd. I can't keep up, obviously, having no vehicle. It was actually easier for me to commute to a parish I didn't "territorially" belong to because of the way public transit works, but eventually I decided to stop commuting, and be honest, and live up to responsibilities of the parish where I belong, territorially, even if that is now a de jure thing of the past.