[GFDuke]

Your copy/paste didnt show what pic but, All joints should be sealed and taped with fiber tape and thinset. You should leave a gap yes but only so your thinset can make the joint complete. If you don't you run the risk of your joint expanding and you tiles will crack at the expansion joint. Not only that. durarock has tapered joints like sheetrock and it helps to kep the tiles even and flat if you fill the joints. Honestly it's all about personal experience in the field of building and remodeling. I've been in this business for 30 years. I've seen people do things differently the whole time. Everyone has their own method and they all have the same results. And, in the end all that matters is a satisfied customer. And that final check. lol