At the end of season one, Galactica sends an attack against a Base Star at Kobol.
At the start of season two, a different Base Star appears at Galactica's location, someplace in (deep?) space I'll call X. (They conjecture that the Cylons had learned Galactica was at X from an attacking pilot.)
Galactica then jumps to a new waypoint, but the rest of the fleet doesn't show up there. They surmise (correctly, it turns out) that the rest of the fleet hadn't had time to calculate how to jump to where Galactica went, and so instead went to the previously-planned next waypoint.
Ok so far, but how does the next part make sense? They know where the rest of the fleet went, but in order to get there themselves, they reason that they need to warp back to point X where the Base Star is probably still sitting, and run calculations from there, before they can rejoin the fleet. Why the frak would they need to do that? Why can't they calculate how to jump there from where they are now?