The energy your building uses comes in two categories: weather-dependent energy use, and non-weather-dependent energy use. The non-weather-dependent use is called the baseload and includes things like lighting, cooking, hot water, and running electrical appliances. All of these energy uses do not vary with the weather (e.g. the amount of energy needed to light a room is the same regardless of how hot or cold it is outside). The baseload is constant over time, staying at (roughly) the same amount each week over the entire year.

The weather-dependent energy consumption is mostly due to heating your building. If it is very cold outside then the boiler will have to work harder (use more energy) to keep the inside temperature at a comfortable level. If one winter the energy consumption of your building is double that of the previous winter, is this because your building is being very inefficient, or because the winter was colder? To properly answer this question you need to include the weather in your energy analysis, which Pilio does.