As explained before, casting spells when your shaman is inside of a tower will have both a positive and a negative consequence.

 

The positive thing is that your spells will have extra range, because the shaman is on the top of the tower, meaning it can reach far away places. This is specially good to cast lightnings, converts and landbridges.

 

The negative aspect is that the spell will have increased delay. What does this mean? Let's take a look at lightning. If your shaman casted a lightning when outside of a tower, she would scream the "shoka", and after  ~1 second the lightning bolt would hit the target. When inside of a tower, splits of seconds will be added to that ~1 second, meaning the target will have more time to react. (specially online, when you are trying to light an enemy shaman form a tower, she will have an easier time dodging). Note that the further away the target of the lightning is, the longest the lightning bolt will take to reach it.