There are multiple methods for pressing quilt blocks. Ultimately, you want an even, correctly sized, very flat block without puckers or thick, hard seams. This helps ensure your quilt is square and makes the quilting process more successful. As a longarm quilter, I cringe when my machine 'thunks' on a thick seam. Broken needles can often throw these machines out of proper timing.
In most cases, I like to press my seams open. No matter how much I press, use tailor’s clappers, steam, or starch, pressing seams to one side just does not often produce a perfectly flat block. In addition, while pressing to one side may help line up your patchwork when sewing a block together, it can create bulky hard seams when sewing blocks together—they seams don’t always work out to nest between the blocks.
Generally, the smaller the block, the more success I find with pressing seams open. That said, when I do press seams open, I tend to use a shorter stitch length (1.6 to 1.8 on my machine). Also, I never stitch in the ditch with seams pressed open. I don’t like stitch in the ditch anyway—I’ve never been good at it and prefer the look of echoing the ditch instead.
In some cases, a modified method of pressing works best. A good example of this is the Road to Oklahoma block, shown here from my Elegant Stars Queen Sized Quilt Kit.
While most instructions on swirling seams I've seen online or on YouTube are illustrated with a 4-patch, I usually just press a 4-patch block open. In general, swirling seams is meant to reduce bulk at the intersection of four or more fabric patches. To do this, unpick the outermost three or four stitches from the seams that are perpendicular to the last seam you’ve sewn. Once those stitches are removed, you can now manipulate the fabric to press in such a way to create the least bulk. Usually, the seam will "tell" you which way to press it, just by how it wants to lay.
The trick to making this work is to verify that the bulk you are saving within the block does not translate to the same or even more bulk when joining blocks together.
With this Road to Oklahoma block, it worked best to press the seam where each 4-patch was joined together (Rows 1 and 2) to one side, away from the HST.
Then, the final seam was swirled so that the center two blocks were pressed open (not to one side), and the outer block (one on each end) were pressed away from the HST.
These Road to Oklahoma blocks are meant to be joined to star blocks made with flying geese. In this case, the seams pressed to one side in the Road to Oklahoma blocks did not match up to any seams in the star blocks, so there was no bulk created.
As always, I’m sharing what works best for me. I’m not sure how much variations in sewing machines, fabric, thread, pressing tools, etc., may make someone else’s experience different. Hopefully though, you’ve found some information in this post that has been helpful.