The one thing that is stressed consistently in the quilting community is the 1/4" seam allowance. Not only that, but a "scant 1/4". Many books, patterns and teachers mention it, but don't always explain what it entails. While there are quite a few patterns/techniques that don't require accuracy, there are many more that require more precise piecing in order to have the pieces fit together like puzzle pieces. Yes, you can "fudge" small errors, but small errors evolve into really big errors as the number and size of the blocks increase in the quilt.
The reason for the "scant" 1/4" is to allow for the thickness of the fabric and the thickness of the thread when you press that seam open. The June Newsletter from Superior Threads has a wonderful explanation of how thread is made, the different types of thread and how thread choices impact your project. The newsletters are archived and it is worth the time to read some of them for tips and good information.
So, here is an easy way to find your 1/4" seam for your machine. Cut three 6"x 1 1/2" strips of fabric. Sew them together lengthwise and press the strip set open. Measure the middle strip (on the right side). It should measure 1". If it is too small, take a bit narrower seam and if it is too wide, take a wider seam allowance. Remember that your 1/4" foot may measure an exact 1/4", but it doesn't take into account the fabric or thread that you are using.