| I use the chisel type buttonhole cutter to clip into seam allowances when I want them to lie flat. You never have to worry about clipping too far, or too little (which is a very common cause of curves that won't lie flat.)
This is also the best tool for cutting the little angle cuts at the ends of bound buttonholes. Again, you will never cut too much or too little.
I use it in any situation where I need a small, precise cut.
They are also perfect for buttonholes, of course.