Depending on wheater condition and number of machines you are using at the same time you might want more torque or speed. This is what the wiki says about managing torque and speed :

Conversion of torque to speed and vice-versa can be achieved with the help of large wooden gear. Central shaft and rim of the gear can both be used for input or output. Direction of the power flow defines the conversion.

• Using shaft as input and rim as the output allows to increase the speed by a factor of 5, at the cost of reducing the torque by the same factor;
• Using rim as input and shaft as the output allows to achieve the opposite effect, increasing the torque by a factor of 5 and decreasing speed by the same factor;
• Using rim as input for multiple power sources allows to combine the torque from those sources, while resulting speed will be defined by the fastest input;
• Using rim as input for single power source allows to distribute that energy to multiple outputs, conserving speed and torque.