Not commenting on the quad tree specifically but I know a lot of reasoning that goes into non-binary tree structures comes down to performance gains from exploiting cache entry size. When each node lookup in the tree is going to trigger an 64-byte load from L1, it's often much better performance to have your tree have 4 or 8 pointers to children in that cache entry rather than two if it means you do on average half or quarter as many traversals.