Use cases for getparameters() & sendparamenters()

Hi , i would like to know the use cases for getparameter and sendparameter. ive looked through the documentations but it seems too generic.

point 2 : Since we cant create custom js file on dashboard level , i did a little trick by creating visual and imbedding my js codes to get the layout i want . problem is , i am not able to create an empty visual. i am selecting table format and setting limit to 0 to get the empty visual effect. but lets say once a filter was set after the initial load. everything vanish. how can we retain it ?

for an example, in js , we can use event listener. in arcadia enterprise. how do we achieve this such behavior? is there any flexibility in creating such custom dashboards?