Most of the formations that Eric set up around the area were concealing and defensive formations, in case of a big fluctuation of energy.
While most of them would most probably crumble with the first attack, they might still give him a precious second to save himself and his life.
With those thoughts in mind, Eric didn't care whether he was wasting his time and precious materials as none of them really mattered, his life was the most important.
One had to have courage and bravery in undertaking life & death battles and situations, in order to come victorious and make steps ahead, that was part of cultivation.
But not when he knew that his life was not even hanging by a thread if he participated, that wouldn't be bravery and courage but stupidity, and suicide.