This is near the end of the approach. Earlier, they were more effective, but it got progressively harder as time wore on.
 
We remember the Alamo not because they beat Santa Ana’s army but because they delayed the enemy for two weeks, which was long enough for Sam Houston to muster his rebels into a force able to meet Santa Ana at San Jacinto. Buying time is an important element of strategy, and the Princesses acquitted themselves well today.

@Dragonmage  
They did, earlier.

How can the ruler of the sun NOT be effective in this situation!? At least show a back and forth before she has to lose!

If you want them to look actually helping instead of these ineffectual beams, force Hasbro to pay animators more so they can properly animate it.

@Kibate  
I see what you mean.

@Tiger beetle  
“It may look useless to someone, but the Empire didn’t freeze, so it wasn’t useless” That’s not really a good argument, because as Amm pointed out, it wasn’t shown that they did anything really.  
It would be like me saying “The world wasn’t destroyed by a supernova today, that means i helped in stopping the sun from exploding”

@Amm  
It may look useless to someone, but the Empire didn’t freeze, so it wasn’t useless. The silly thing is calling Tia and Luna themselves useless. That’s what I meant. But I guess they look pretty weak while compared to the power of this snow storm.

@Tiger beetle  
It’s silly to call someone that looks like they’re doing useless things useless? Seems pretty intuitive to me. This is actually more a problem with the episode in that we’re told they’re helping and shown that they’re useless. Which is pretty much on the nose for Celestia in general.

@Amm  
I see. But the fact is, Celestia and Luna are helping and people still call them useless. That’s just silly.

For some reason, the sentence “Searchlights over London” came to mind!

@gingerninja666  
People are mocking how they looked completely useless and ineffectual while doing it. Not that they failed against it.

Thanks you two, you are being REALLY helpful

@Tiger beetle
 
Exactly. In the story’s continuity, if her and Luna hadn’t done this, they would’ve lost.

I don’t think ‘‘Uselesstia’’ tag belongs here. She was trying to slow down the storm and she contributed to the final solution.

@gingerninja666  
Yeah. It struck me as an extremely temporary measure to buy a little time.
 
@JP  
I think they addressed that point in the show. When Sombra was in power, the Crystal Heart was hidden, not destroyed. I think the wild weather would quickly overpower a shield without it intact.

@JP  
They’re not Shining Armor, the opposing storm is sentient and actively malevolent (and probably also chock-full of Windigos), and they don’t have time - it’s not known how long it took to erect shields over Canterlot and Crystal Empire first time and the storm is in the city already.
 
Also animators aren’t paid enough to properly showcase the power and how it was futile against the storm.

@gingerninja666  
So the Crystal Empire is Oklahoma then?

@JP
 
It’d probably shatter it.
 
People are mocking the fact that they’re beaten by weather. This annoys me because they make it clear the weather isn’t normal. IT’s wild, has a mind of it’s own and seems to control the entire north of the WORLD.

“I attack the darkness!”

Royal princess laser light show

THEY DPO SHIT!!!!!
 
And it is admitably against a wild elemental force that cocvers northern equestria. So while they could not outright stop it, it is still a rather significant force.

Couldn’t they just have erected a force field around the city? Shining Armor could do that alone, surely they working together could have created one big enough to cover the entire place?