Answer:
It is often not necessary to completely distill the higher-boiling fraction because the desired component or components can be separated and collected at a lower boiling point. This is achieved through fractional distillation, which allows for the separation of components with different boiling points by taking advantage of the temperature gradient within the distillation apparatus. As the mixture is heated, the component with the lower boiling point vaporizes first and can be collected, while the higher-boiling components remain in the distillation flask. This allows for the separation and collection of the desired components without the need to completely distill the higher-boiling fraction, which may contain unwanted impurities or components.