You can read more about this strategy at here.
At Town Hall 7 in Clash of Clans, people start joining Clan Wars more than at Town Hall 6 because of the sweet loot bonus. You can earn up to 300k Gold and Elixir for every win Clan War, that’s pretty sweet right? Sometimes, you can even earn hundreds DE, that’s much better and easier than farming outside in hours.
Dragons are the most powerful troop at Town Hall 7, especially the Dragon level 2, which can destroy any building with just 1-2 hit.
The number of buildings which can survive more than 3 hits of Dragons is very small. As far as I can remember, it’s no more than 4 buildings except the Storages.
With that being sid, at Town Hall 7, If you want to use the Mass Dragon attack, especially after the new update (Town Hall 7 players can buy the third base Air Defense), I strongly recommend you guys get the Lighting Spell to its maxed level as soon as possible, brew 3 spells, bring them into the battle and destroy the hardest-to-take Air Defense, snipe the Air Sweeper or another Air Defense with your Hog Riders or Balloons in Clan Castle. Don’t use your own troops to finish this job. Balloons and Hog Riders with maxed level from your friends in Clan are much better.
After taking down the Air Defense, If you want to completely bully a th7 farming base, you should drag and drop your Dragons in a line. Don’t place then in just 1 spot. If they hit a trap horde, you will be fine. Also, you should know about funnel If you don’t want your Dragons go shopping around the enemy base and get hit badly by the enemy ADs and Air Sweeeper inside.
Also, don’t attack from the behind of the Air Sweeper If you don’t have the Rage Spell or If you don’t know that are you doing. The Air Sweeper can always push your Dragons back badly and sometimes you even can’t deal enough damage to a 50% win.
Take care guys! See ya!