When I can I press open. Why? Because I quilt my own quilts and the flatter the top the less it interferes with my quilting stitches. Pressing seams open keeps the work flat as possible. That flatness also betrays any errors in piecing early in the process so I can quickly fix what is wrong.
At times you do have to press to the side, and when that happens I don't obsess about it.
I do not nest seams. I don't think simply nesting is the key to good seam intersections, partly because the bulk of the pressed-to-the-sides seams interferes with the ability to see where the intersection is and control where it stays when the presser foot hits the fabric bump.
I have found I get much better results pressing open and pinning seam intersections with very fine pins.
Not every block needs to be precision sewn, but when they do, pressing seams open is a help. Nothing bothers me more than a work that should be accurate but isn't. We put so much time and $$ into our quilts, it is a shame when the workmanship undermines the vision!
I suspect there are a few reasons quilters fail to be accurate when they should be: maybe they don't know how, maybe they don't enjoy the process of construction (I love it so am happy to take the time), maybe they don't have the tools and/or setup to work comfortably and consistently.
All those things can be remedied.