Small Bomb Traps

Probably one of the most commonly misunderstood traps in the game is the small bomb trap.  They have exceptionally low damage and can't even kill an archer.  Most people find them utterly useless and do not upgrade them, or will throw them around randomly on their base.  Some will try to lump 3 or 4 of them together to give them a little more punch.  This is, however, not the way this trap was meant to be used.  The small bomb trap has one sole purpose: killing wallbreakers.  And to kill wallbreakers, they need to be placed:
1) In areas that people normally try to enter your base from
2) One tile space away from your walls

Take the following picture:

This picture is from a replay of my base being attacked.  There's a narrow gap between my barracks and elixir collector where people usually tend to send bombers in, so I placed a small bomb there.  You need to place a one-tile gap between the bomb and the wall, however, for the bomb to be effective.  The reason being that the small bomb has a one-second delay, and if you place it too close to your wall, the wallbreaker will explode before your small bomb has a chance to kill it.  By placing it further away from the wall, the wallbreaker will trip your bomb earlier, allowing it to go off before the wallbreakers detonate themselves.

In my experience, the small bombs do not work perfectly to kill off wallbreakers.  In the picture above, 2 of the wallbreakers did manage to explode, but the other 2 did not.  Ultimately, it was enough to keep my wall intact, and it did delay the enemy's kill squad longer than they were probably expecting.  So please keep in mind when designing your base that the small bombs are meant to be placed at locations where you expect your opponent to enter from to kill wallbreakers.  Sometimes these little traps can throw off an enemy's funnel and help to defend your base a little better.