In my first quilting class I was told to iron seems in the direction of the darker fabric or toward the least bulk. But is there a real reason why I can't iron my seams open?

I'm not real experienced at quilting, but I guess it depends on what you're doing with the seam. If you're doing one of those star thingies, then open works best, less bulk, but if I am going to match blocks and want a perfect join, then I press seams to the dark, so that when I am matching the seams they just meld right together. Hope you understand that.

They tell you to press the seams toward the dark so when the batting is layered on the dark fabric does not show through( thanif you pressed toward the lighter fabric) . It is a pbit faster to press to one side rather than open.
Personally I press open most of the time( quilting for over 35 years) . I like a really flat block.

Kryssa, there really isn't a reason not to iron your seams open anymore, and although I've read the reason they were customarily ironed to one side, I don't recall what it was. A number of quilters iron their seams open because they prefer the absolutely flat look it provides. Some also believe free motion quilting is easier with flat seams. I believe there is some concern that seams are more likely to get skewed when ironed open, and that intersections of blocks require more special handling. I've done both, but I'm not experienced enough to have much of an opinion either way. When I have a little extra time, I'll try to find the sites where I originally got this information and post the links. Have fun!

Quilters choice.

Clothes have seams pressed open unless they have been serged.

Although, if my light fabric is thin, I find it's best to press towards the dark.

I think it's what ever works best for what you are piecing.

One reason I was told many years back was that if you leave your seams open the batting can come through the seams during a wash. I wonder if todays batting would do that?

A second reason is ease of butting up the seams. Matching your seams is so much easier.

Of course ironing towards the dark is always a reason as well.

I've heard some say a quilt lays flatter if you iron the seams open, but I was taught to iron them to one side, and I'm afraid of the quilt police, lol.

This history of the seam pressed to one side originated when quilts were hand stitched. Pressing to one side strengthened the seam. Now that most quilts are machine sewn that is no longer a necessity.

My thoughts on the pressing to one side (light to dark) ... when you sew two sets together, the points line up (nest) better when one goes one direction and the other another. Seams ironed to left, nestle to those ironed to the right... not sure this is coming out right.. but it sort of locks the seams and keeps the points aligned. Correct me if I am wrong. :)

One reason to press a seam to one side instead of open:

If the stitching failed, then there would not be a "gap"

Also much easier to Stitch In the Ditch if pressed to one side. No hard & fast rule - whichever feels and looks best to you.