When a player is in the position such that to pass would end the bidding, he is in the balancing (protective) position.
In both examples, South is the player in the balancing position. Since partner may have a fair hand, but the wrong shape for an overcall or take- out double, it is often advisable for the player in that position to bid or to double for take-out, even on slender values.
In the second example, it is particularly attractive for South to take some action. This is because East-West’s known fit in diamonds increases the chance of a North-South fit somewhere whilst minimising the risk that action by South will push East-West into a better contract.