This has been asked in How to layout parts first and then backfill a schematic? but I’m hoping to revive it as modern manufacturers and KiCAD’s capabilities have now made large BGA based designs very doable. The problem is, you get a processor or FPGA with 1000 IO’s and a bunch of connectors to route to cleanly, but the schematic has all the pins listed in the wrong order. You do your dogbone fanout and have an array of pins fanning out on the front, bottom, and inner layers, but then you have to go in and change each pin label to be sequential with the schematic side-by-side. It would be more efficient to assign nets on pins in PCBNew and have the schematic follow these changes.
Upvote this by giving a thumb up: https://gitlab.com/kicad/code/kicad/-/issues/1950