If you really want precise 1/4" seams, then you have to check them. Here's a tutorial that shows the standard verification method. remember to use the same ruler you are going to use with your project:
http://www.quiltingboard.com/tutoria...ce-t89997.html
Once you figure out where the scant 1/4" is on your machine, you can adjust the needle and use your foot and/or use something stuck to your machine bed to guide the fabric (like a stack of postit notes, or a piece of moleskin). If you always use the same weight fabric, and same weight thread, then you really only need to do this once. If you change something, like the thread weight, or use a different fabric for a project, then you need to do a recheck. It really only takes a few minutes and with a complex design, it makes a huge difference.
Also, remember that pressing can also make it or break it. If you press and get a tiny fold in the seam, your patch will be off.
My thought is that it takes the same amount of time to sew a seam that's the correct width as to sew one that's sort of close. I think you really save a lot of time when your pieces fit easily vs. having to ease or rip.
A great book on this topic is "The Art of Machine Piecing " by Sally Collins.
http://www.amazon.com/The-Machine-Pi...ollins+machine
There are lots of copies available on Amazon for a dime. Even with shipping less than a magazine!