When creating general pattern for different usage, there is a need select which patten pieces to print.
I have shirt pattern, which have both long sleeve and short sleeve included. When printing with long sleeve there will be along the sleeve itself cuff, cuff interface and placket pieces. These are not needed with short sleeve.
Some times there is a need to print just interfaces or linings,
Of course this functionality can be achieved with deleting the unnecessary pieces, but a selector would be easier.