Astral Waypoint has a lot of uses:
It allows Wayfarers to have their units wherever they want as this card allows your other units to create a point for yet more friendly units to join.
They are a virtual spot for your high threat units to exist, like Celeste and Boldo, and for the purpose of considering threats now your opponent needs to not only consider their current place but the Astral Waypoint as a potential place they can instantly be, forcing your opponent to have to deal with a threat from multiple, hard to predict angles.
In addition it is an escape route for Celeste, if she gets in a bad position she can use Astral Waypoint to flee.
It’s also another “blocking” tool, used to block opponent summoning spots and/or movement paths.
Finally, Astral Waypoint can often be used as a shield, to protect a side of a unit that just advanced.