Pressing to one side was done originally due to it prevents the batting coming out of the seam. I think that was way back before the batting making technique was perfected. I press them to one side and if you are stitching in the ditch you'll notice it's easier than if they are open. I think for the most part now days, it's a preferrence; like just about everything in sewing and quilt making. I'm not sure if it makes a difference if you ever plan on entering them into a quilt competetion.

i was doing some blocks for a cause last night that specified press open and have to agree with this! I suppose over time it gets more natural, but it took me extra pressing time to get the flat look I like.

I press to one side unless there is a compelling reason not to. First I was taught that way, and I also would not want any batting showing on the seam line. I do hand quilt and it seems to work for me. I'm not sure the comparison for strength on open seams between clothing and quilts is particularly relevant. Very few pieces of clothing will be around and used in 25-100 yrs., but a well made quilt probably will.