> if looking at a file that might be renamed and stop updating (i.e. log files that are rotated). Without a filename the file descriptor is followed so when for instance access.log becomes access.log.1 your display keeps following access.log.1 not the new access.log which is probably what you want.

I believe that's true if you name a file as well (just tested it on Ubuntu). You keep following the original file you named, even if it becomes renamed; you don't follow a new file by the same name.

Using something like "watch -n5 tail filename" polls every few seconds to show the bottom of a file, and goes for the current file at that filename each time.