You don't necessarily have to press the seams this way but I think it looks cool. On the next photo you can see two different ways of pressing the seams, and they both work but one has a little more bulk then the other one. Sometimes I might want to press them all one direction to prevent shadowing where a light color is going to show dark colors behind it. It's your choice.
The same kind of procedure applies for sewing together the hexagons in this case you again only sew up to that quarter-inch.and that allows you to move the seams this way and that so they line up properly. Good luck and I hope this helps.