As we know we can hide the unused fields (dimensions, measures and sets) from the data pane of the source. If we're using any of the dimension/measure/sets in our worksheets then hide option will not be available its means we cannot hide it unless we remove it from the canvas. But in case of parameters whether you use it in you canvas or not, Hide option will always appears. I think its should not be. I'd suggest its should be fixed.
In below example, I've used Sub-Category in the canvas and trying to hide the field though I cannot which is obvious and logical.
Same for Discount measure and Sets (Top Customers by Profit)
But while using parameter in canvas still Hide option is available that should not be.