Pressing Seams Open, Pressing Seams to One Side, Pressing Seams to the Dark Side… stumped like me?
Here is what I found....we press to one side to allow our seams to nest together for precision piecing, and this also reduces the amount of pins we need to use. This is definitely less time consuming and seams tend to match more perfectly. In addition, pressing seams to one side will create a high side and a low side, which makes quilting in the ditch way easier and neater. But you can’t always follow pressing to one side as THE way to press seams, as sometimes when pressing to one side, seams will bulk up creating a lump of fabric. This happens mostly when diagonal seams meet. In these cases, pressing the seam open will give a smoother, neater finish. 
Pressing seams open will make them flatter; points will be sharper, crisper, and more accurate. When your seams are pressed open you can always see where a point is when you are sewing the next seam and you can sew exactly through its point. In this case were you to press to one side, this will invariably hide your point(s), so you are sewing blind, and may or may not go exactly through the point.
Another rule I found for pressing seams, is to press them toward the darker fabric and will avoid creating a shadow on the lighter fabric. But when you need to nest seams, you can’t always follow this either. Then there is ironing vs. pressing!! OH MY!!
In the long and the short of it, what I’ve discovered about the best way to press you seams is that pressing all depends on the fabric, block or design you are sewing. So for precise pressing, its most likely you’ll use a combination of all of these pressing methods.
