Your bike’s geards are designed to help you keep a consitent cadence , allowing you to pedal at maximum efficiency. Rifing conditions such as wind resistance, terrain and groups dynamics are contantly changing, and you should adjust your gera ratio accordingly. A cadence meter provide a steady gauge of how fast you’re pedaling.
You should anticipate conditions that will affect your effort level so you can shift before you actually need a smaller or bigger gear. Changing gears when ther is less pressure on the pedals allows for a much smoother shift and less wear on your drive train, especially when you’re shifting the front derailleur.