the blue tape can stay on longer without leaving glue behind when it's pulled up. Mostly it's the idea that you don't have to worry about the edge of the cloth while wetting out and when it's partially cured the tape helps pull the cut cloth as you run the razor along it at an edge.
I was wondering about Erics recommendation in the manual for 3" tape only on the interior and 4oz cloth on the outside. My experience has been that plywood only on the interior bottom panels allows for waterstaining cracks between the tape. Or at least on kayaks with very wide bottoms,,,the Merganser bottom panels aren't very wide and they have more v so it's not as much an issue as it would be in a Chesapeake aft compartment. Tape makes every thing go fast but once you start looking at tape AND cloth it starts making sense to use only cloth and cut strips as needed. None of these permutations are that significant in the big picture,,but they do keep one entertained with the possibilities.