This way, the expressions are always written correctly, so that users are getting correct information. If you want to allow them to use charts other than a straight table, you can add a fast change to let them choose a different type of chart.
Set Analysis is a techie thing : it is NOT for users
Do either simple selection (easy way in QV). Users will see a lot with that simple way of doing.
Create Alternate States : same thing as above, but with several separated selections on the same dimension (very useful to compare things)
Create Set Analysis with variables and let the users modify the variables through dedicated QV objects (Calendar, input box, sliders ...). For example, you will have a measure for data X months ago (next to the data of this month): the user may choose the X and it is enough (no need to create the Set Analysis)