NewzScape scans all the newsgroups on your Downloader window in the order that they are listed. When it finishes the last newsgroup, it resumes at the top of the list with the first newsgroup. At that point, you can use this setting to tell NewzScape to pause. The reason why you would do this is to not be a pest to the Usenet server. Once NewzScape has finished all of your newsgroups, it may be a while before any new posts show up, depending on how popular your newsgroups are. During this time it is not necessary to constantly badger the server.
If there are no new posts in any of your newsgroups, and you have the pause setting set to zero, NewzScape will rapid-fire commands at the server asking it if any new posts have arrived. This is bad manners, and might even cause your ISP to send you a warning. So, ideally, we want to pause after the last newsgroup before we have NewzScape scan them again.
If you have a large number of newsgroups on your Downloader that get a lot of traffic, NewzScape may have to struggle to keep up with them all. In that case, it is still a good idea to set your pause minutes to one. There is no way of predicting when new posts will arrive on the server, and if you leave NewzScape running 24x7x365, it is likely to catch up at some point.