Why 1/4" seam? Well, it has to be "something" uniform, so that blocks will fit together. A wider seam would end up being too big, for some of the smaller pieces. A narrower seam would compromise the construction. I wonder how long ago, the 1/4" seam started. I do know it wasn't used everywhere, as my grandmother's quilts had wider seams (never thought to measure them).
Any seam allowance will work, as long as you're consistent. I recently made a dog bed, using 1/2" seams (to make it more dog-resistant). Yes, it had points - it was a pinwheel star pattern. Yes, my points ended up exactly where they were supposed to be.
