It is such a tricky issue.
I live in a rural village / market town now, so of course for us, catchment areas are necessary. It would be impossible for me to drive 5 miles to the next town to send my child to school.
But, in the town I came from each school had a designated catchment area, and the catchment school wasn't necessraily your closest - for example, I had to drive past the local junior school to get to my catchment junior school. Also, the town I lived in was a post war / 'growth' town, so had areas of large council housing. These were the worst schools, and most people tried to avoid sending their children there. Then there was the big modern estate, where everyone wanted to live, and not enough schools and everyone moaned because their child could not go the local school.
I am also unsure of whether siblings should take priority over children in catchment. I know of a few people who chose to send their eldest children out of catchment, but then did not get their subsequent children into that school (as at the time, siblings did not have priority) and boy did some of those parents moan, but then I think you knew that when you applied out of catchment that you were taking a risk. And further, if the sibling takes a place from a catchment child, then the catchment child has to be driven to a different school and this increases transport and so on...
Of course, in an ideal world everyone would just send their child to their local school, and catchment schools would be made of different socio economic areas. This would reduce traffic in the mornings, be better for the environment and better for making local communities. But unfortunately, in my town at least, the socio economic areas are not mixed, and the best schools are in the best catchment areas and the worst schools are in the worst areas, so everyone scrums to get into the best schools and then moans when they can't.
Not sure what the answer is tbh.