The big reason I prefer to press to the side is that I have serious trouble matching up seams that are pressed open, and there is a very high probability that I will have to rip out and re-do. On the other hand, it is easy for me to match up seams that nest. The other reason I don't like pressing open is because the seams don't stay flat and open for me, whereas seams pressed to the side stay right where I've pressed them. I will consider pressing open when a pattern specifies to do so, and I have taken to pressing open the last seams of some sampler blocks, where the rows are sewn together.