I press to the dark side whenever possible due to batting "leaking" through and also for strength of the seam. Think about pulling on a seam that's been pressed open as opposed to pressed to a side. Stronger when pressed to the side.

Pressing to one side towards the darker color is the most popular choice.

Although I open seams for clothing, I generally press to the side as I find the open seams, over time, tend to open up the tiniest bit and a bit of batting eases out unless you use very tiny stitches. When the seam is pressed to the side, it sort of covers up the seam.

I press to the dark side

It depends on the psttern for me. I'm with "qltncat" about the block dictating what to do.

I started pressing ALL of my seams opened after doing the 14" Bear Paw blocks (one block had over 100 pieces). For me I have more accurate and flatter blocks. I've also spoke to the person doing my LA'ing and she agrees that it's easier to quilt when pressed open.

Dear quilter, I have two machines. I use one to stitch the initial seams and use a wooden dowel and open all of them, of course, I eventually have to iron them as well. The machine I use for quilting has the even feed foot and because I have initially opened all the seams the machine works much better with a lot less problems stitching. It takes a little more time to do this, but a lot less shrieking as the poor machine tries to quilting over too many layers. God bless and give this a try. Quilting Joan

Glad you mentioned strength of seam. I was just going to say that. I think with the seams being pressed open, it would cause more chance of the seam splitting open. Pressed to the side won't.

Stress on a seam is ....stress on a seam ... pressing one way or another does not help. If in fact it was an issue , the fabric could tear then before the thread , I would rather repair a seam then a tear in the fabric.
Test it for yourself on a sample !

I press to the dark unless I'm paper piecing, then I press open to reduce bulk.