This elixir, which is no longer in the game, was meant mostly for splitpushing, but the health bonus may prove effective on any champion.
Siege Commander guarantees stable increased damage output to towers when minions are around.
Elixirs were often bought towards the end of long games when builds are all completed and the extra gold continues to accumulate. They can also be bought mid game to give a temporary stat advantage during ganks, teamfights. Ruin is also useful for split pushing any time, as it boosts damage to turrets.