Some Components have values that need to be set before use. Thats what parameters do. Usually they don't ever need to be changed. For an example, look at the THC component. It is for use with the Mesa THCAD hardware. Each of these boards is individually calibrated and the calibration data is applied to a sticker attached to the board.
So paramaters are used to set this calibration data as shown in thic code excerpt.
Code:
// Parameters
param rw float vel_scale "The scale to convert the Velocity signal to Volts";
param rw float scale_offset "The offset of the velocity input at 0 volts";
