If you have an instance parameter in a family (shared or family parameter type) and, after starting the "add process" by either using a ribbon tool or by dragging a type from the Project Browser, you then change the value of that instance parameter BEFORE placing the instance, you will find that the value you entered becomes the new default value for subsequent placements of that family. (For shared parameters, it will be the default for the subsequent placement of any family of that same category using that same shared parameter.)
That can be handy if you are placing a number of objects where you want the same instance value, but there may be times when you would like to have the initial value reset back to the default value specified in the family. Here is a tip I picked up in a post by CADastrophe in the AUGI Revit Architecture - General Forum.
You can reset the instance parameter back to the default value by starting the add process and, before placing an instance, using the Type Selector at the top of the Properties palette to choose a different type. It is not necessary to actually place an instance - you can escape out of the add process and the value will be reset to the default. If you do want to place an instance, you can change back to the originally selected type (assuming that you started with the desired type).
Changing the value of an instance parameter AFTER placement (and ending the add process) does not change the default value for the next placement. If, however, you select an object and use the Create Similar tool from the Modify|Object Type ribbon tab on the Create panel or from the right-click context menu, that will set the future default value for any instance parameters to the values of the selected object. These can be reset to the defaults using the technique noted above.