Mary Ellen Hopkins uses what she calls her PPM (personal private measurement) when she pieces and she swears that you don't have to stick to a quarter inch, as long as your seam allowances are consistant thoroughout the project. Her recommendation is to use the seam allowance you are comfortable with. I haven't tried her method (I'm a quarter-incher), so I can't testify to it. But she is a prolific quilter and has written a boat load of quilting books. So I tend to think she is on to something.
However, pieced block instructions are almost always based on a quarter inch seam allowance, so a change in seam allowance with change the size of the finished block.