Hey @shmu26,
Recent Posts are all the threads/posts that were created in the last 72 hours, regardless if you viewed/read them, while if you click on the New Posts, you will only be shown the threads/posts that were posted since your last check, basically posts which you haven't viewed/read. I'll rename the New Posts tab to Unread Posts to make it more clear.
@Jack keep both categories.
I am very busy these days and i can't visit the forum often.
Both categories have helped me to save time to find all new threads that were posted while i was away.
Great job