Getting reputation for the new factions is going to be beneficial in different ways. Earning reputation towards the factions is going to help you unlock Pathfinder in Kul'Tiras and Zandalari. Pathfinder is nothing new so i decided to include it in here. Pathfinder will give your character increased mount speed and its account wide. Also gaining reputation will allow your character to buy gear, from a vendor, equal to Heroic dungeon quality.
The guide works great (of course expect a) BUT, after reaching 120 there should also be a guide to open and explore the remaining areas. Also, sometimes when multiple objectives are required, the guide forces you to follow in the order the guide prefers and if you don’t the objective is not rewarded. Gotta start catching up on the followers guides also. All in all, the $47 a year in-game guide is well worth it.
Something to keep in mind as well is that this will make enchanting materials more valuable, since it is likely most players will now simply scrap their boe greens instead of getting them disenchanted. Also redundant dungeon/raid gear can be scrapped rather than traded to the (guild) enchanter in the run. Less stuff gets disenchanted, meaning there will be less ecnhanting materials, meaning their value will rise. All the more reason to DE rather than scrap as an ecnhanter.