I hope the title isn't a spoiler anymore. Anyway, I am currently rereading the books and watching the show more or less in parallel to see the differences. I understand some (mainly to keep the cast and locations smaller), though for others I don't see any reason at all. One if this is in Season 4 Episode 4 or 5,
where Jon Snow revisits Crasters keep: First of all, in the books Sam swore to Brandon to keep it secret that he goes north of the wall. In the show Sam tells Jon about it and is overheard by one of Boltons officers (initially I thought this is the shows representation of Vargo Hoath as he was in Harrenhal). They then set out to Craster keep to kill the deserters and Boltons guy just joins to get Brandon. Brandon then kills this guy through Hodor and is convinced by Jojen not to talk to Jon as he would take him back to the wall.
I don't see any purpose in this whole plot arch. I didn't watch Seoson 5 yet, but I don't mind any spoilers if it would explain this.
There are others scenes, which I don't understand the show creators intentions like:
The fight between Brienne and The Hound, they could have gotten the hound wounded in the inn, just like in the books whereafter Arya leaves him to die as well.