Lightning, the Swiss Army Knife of Spells
The lightning spell is a very versatile spell.
You can use it to take out Clan Castle troops that you couldn't lure out or didn't realize where there.
You can use it to attack a Dark Elixir storage or Drill and earn some sweet black oil.
You can use it to take out the last hit points on that stubborn building to get you to 50%
You can use it to take out a group of Builders Huts (for a 50% win), because many people cninjaer them together and a higher level lightning can take them out with 1 hit.
You can use it (with a few more) to take out a pivotal defense tower like an Air Defence, Mortar or Wizard Tower
What else can you use it for? Let me know in the comments...