Just like with the gears of any mechanical apparatus, bicycle gears serve the purpose of increasing the efficiency of your bike’s function. The gears of your bike will considerably allow the power source “the rider” to maneuver at an efficient pace while the power or energy put forth is converted either into a greater or slower speed, whichever is more reasonable contingent to the amount of resistance at hand. To put it simply, the gears of bicycles will allow you to maintain a relatively steady pedal speed or cadence and to exert an almost equal level of effort, regardless of the inclination of the terrain you will be taking.
The gears of bicycles will essentially control the significant relationship between the cadence or the pedal rate of the rider and the rate by which the bicycle wheels turn.
For going up steep landscapes, bikers gear down in order to decrease the amount of pressure which has to be applied to the pedals while still being able to resist the greater pull of gravity. This gear allows the rider to push the pedals several times in order to turn the bicycle wheels once. With this, the cyclist may need to give up speed in order to save effort and to avoid muscle strain, which is likely to happen when the rider has to exert greater effort to push the bicycle further up when not gearing down.
Consequently, when travelling on flat or sloping downward terrains, cyclists choose a gear which allows them to turn the wheels of the bicycle several times for each and every pedal turn. Thus, your pedaling will effectively push your bicycle forward instead of just having the pedals spin pointlessly and uncontrollably.
In both circumstances, your cadence and the energy you exert on pushing the pedals may feel just about comparable, because the gears considerably make the necessary adjustments that will allow you to control the distance covered for each pedal turn.
To put it all together, having gears on your bicycle will efficiently allow you to keep pedaling at a pace and effort in which you are most comfortable with, whether you are going up or down a steep slope.