What is the main benefit of preflight weather assessment for IFR flights?

The main benefit of preflight weather assessment for IFR flights is that it helps in making informed routing and fuel decisions. Understanding the weather conditions before departure allows pilots to evaluate potential hazards such as thunderstorms, icing, low visibility, or turbulence that could impact their route. This assessment aids in choosing the safest and most efficient flight path, allowing for adequate fuel calculations by anticipating changes in route due to weather and ensuring that there is enough fuel for the journey considering alternate airports if necessary.

In preflight planning, having access to up-to-date weather information allows pilots to avoid areas of adverse weather, possibly leading to changes in altitude or routing that enhance safety and operational effectiveness.