In general, it will remember the last post you read. You should only need “Jump to New” if it’s a thread that you haven’t read since before the new software was set up.
When the new software started, I remember an option to mark all as read. That basically told the software that I was current on all threads and accordingly, I haven’t had to use the “Jump to New” very often. I have found it necessary when someone resurrects an old thread.