pressing seams to one side is a residue of hand piecing.

I iron them open sometimes, but you run the risk of the batting showing through.

You press the seams to one side so you will not have gaps for the batting to 'leak' through. The gaps are 'teeney' but remember we used to sew by hand. If you are doing a star block, it will be flatter if all seams are 'to the right' then there will not be a bunch at the center.
It is also much easier to press to one side, you sort of gently pull the fabric in one direction and push the iron in the other and you will have nice neat seams that are completely open.
Keep in mind that you really want to press more than iron, in other words, press the iron down but do not push and pull as you may distort the seam, particularly if youhave something on the bias.
Mary

I press to the sides 99% of the time. There are certain blocks that have to have the seams open to lay flat. When I press the seams open I can see the thread and I don' like that look. If you press the seams to opposits sides you have two layers when you join the blocks you have two layers on each side of a joined block. When you press the seams open and join to another block you still have two layers. Again as several have said, Do what works best for you. We'll keep the quilt police away from your quilts. :lol:

Hello Kryssa, I was taught that a seam pressed open might spread bulk, but is weaker - a thread can easily be snagged (say by a buckle on a child's shoe or broken zip in clothing) and the whole seam could be ripped open with fabric actually tearing in different directions thus making a major repair necessary. Strong seams are a must in patchwork, hope this helps :D

If the block has a lot of seams I press them open. I always fan out my intersecting seams if I press to one side. The block will lay much flatter by opening the intersecting seams.

Wen you press all seams to the same side, it will evern out when you butt two seamed pieces together. also when you quilt (and in the old days, it was ususally by hand,) the quilting would go on the seam side and make a stronger seam as it was sewn like a flat fell seam (I am showing my age)

Mary

I only press to one side if I am using lights and darks. I feel better knowing my dark side is not going to show up on the light side if I press towards the dark but otherwise I like an open seam.

I press my seams open. Seem to lay better in my opinion.

It makes the seams stronger,