User blog comment:Zathronas/Analysis by an author: Antagonist, Cinder Fall/@comment-12227301-20131219212159/@comment-3146930-20131220205748

Because Hunters are the only class of police force with the ability to actually stand in their way. Destroying important parts of the city and a large group of Hunters is just a means to an end.

Now this could just be speculation on my part, but I think their ultimate plan is to somehow become masters of the Original Dust. This type of Dust is said to be what humans were born from and most likely, all other beings were born from this too (including the Grimm). Now Roman doesn't seem like the kind of guy to think this up on his own and once his part of the plan is complete, Crimson will most likely turn on him in a second. I also don't think Crimson is the Big Bad of the series and there is at least one person above her pulling all the strings. Anyway, this Big Bad most likely promised the White Fang a type of leadership in this new world order, as they plan to use Dust as a way to make a new world.

Now back to the explosives. Beacon itself may sit on top of some kind of important artifact needed to pull this off. I say this because in the first episode, we saw four original kingdoms and later in the series, the initiation for Beacon revealed a large castle-like structure in the forest; possibly one of the original kingdoms or at least a part of it. However it is right next to a school of Hunters and Hunters-in-training. As a result, you need a big enough distraction to occupy everyone's attention and maybe even kill some enemies along the way.

As a result, as stated in another post, they would take out power stations, any means of transportation, any combat schools in the area, and the location of the festival. As a result of such actions, any surviving Hunters would be busy trying to control panicked crowds of people, as well as fighting off members of the White Fang or possibly Grimm that would be used to slow down Hunter progress. As I said, they would want to kill these Hunters because they are the only legitimate threat, as the cops are useless from what we have seen. Even two students managed to successfully stage a sting operation when the cops were nowhere to be seen. Then Crimson or her group could easily slip in, steal an important item, and be out in no time during all the panic. Of course we don't know a lot of factors of this world so there is plenty of room for change to this theory.