Accurate/Precision cutting always makes for better results from beginning to end.
As does precision seam allowances.
When I started back quilting, one of the first patterns I followed was an Eleanor Burns.
She had you stitch a seam, and told you the size of the unit.
Add another piece, and measure again.
It seemed like a bug-bear at the time, but it sure taught me good habits.
I was lucky to land upon that book .... as not all her books/patterns were written with such intensity!
I have kept those skills in my repertoire.
I'll look forward to seeing what your butterflies become!