Silly maybe, but I'm just the messenger. If you don't do it, the edges of the tape look really dirty after a while because the adhesive hangs onto any stuff that comes its way. (My white tape now has "black" edges.) They're only suggesting a very small bead of course, because the tape and backside adhesive isn't very thick. Jim made a good point that any caulk is counterintuitive to the idea of using the tape.
Since it's on the roof, there's no real reason to worry about it though, because nobody but you will see it up there.