One of the important things to do when planning a series is to consider how the budget should be spent. Rather than spreading it evenly over the episodes, most producers allocate more money towards the start, middle and end of the season (and if it's an American production, towards the Sweeps, wherever they may fall). That way, you can keep the audience's attention by letting big stories (be they huge battle scenes, exciting explosions or just big-name guest stars) flare up every so often, rather than having a run of episodes that are equally flat. Examples of Bottle Episode include: