TODAY'S POSTS vs NEW POSTS what is the difference?

[Xfaxman]

Please tell me why there are two things that appear to do the same thing.

Thanks in advance

 

[RickB]

Today's Posts goes back 24 hrs.
New Posts goes back to the time of your last login.

 

[aczlan]

New Posts is all unread posts going back ~10 days, Today's Posts is the last 24 hours.

Aaron Z