Shelter from the Storm can be situational. It allows you to protect a unit from damage but provides no protection from tactics beyond the shield itself, so if your opponent has a unit with two tactics icons, they can still keep the sheltered character from striking. Even if the opponent can't do that, there's a fair chance they'll have other targets for their tactics icons, guns and events.

Remember too that the event can only be used if there's a Hoth objective in play. It's rare for the Dark Side to use Hoth sets, so to enable the event, the Light Side needs to play them. Unfortunately, most of the Hoth sets have frail, uninspiring units and few characters. The characters they do have generally favor defensive guns and tactics rather than bombs, which is thematically appropriately but hamstrings their ability to close games. The characters' icons also tend to be edge-enabled.

The other cards in Preparation for Battle are a case in point. None have bombs, and every icon in the set except the Tauntaun is edge-enabled. While the objective works with the abundant Shielding, the only valid target for the event in the set itself is a one-health unit whose sole purpose is to die to provide a shield to someone else.

Way back in the day (when this set first came out) it was a very useful cog in a LS shielding deck.  Deck ran Core Luke, Core Han, Core Obi-Wan, Secret of Yavin 4, and this set.  Getting Luke or Han shielded (with Prep for Battle out) early in the game did work.