It all boils down to the grid of the block. You need a different setting when making a 3x3 grid block than when designing a 4x4 grid one.
9 patch (3x3) vs. Sawtooth Star (4x4) as an example.
You can see the problems if you have setting for an 8" block, graph paper set on 3x3, and a snap grid set to 16. Try splitting (bisecting) any of those squares with a line - it's not going to snap.
So you always want those 3 set-up options to be in sync with the grid/size of the block.