Working with a Tablix where you are setting the Row or Column Visibility of a Row Group or Column Group, you have a couple of options:
First is a radio button selection with three choices: Show, Hide, and "Show or Hide based on an expression". This last option, though very powerful, is difficult to understand and can be make 100% more clear to the developer simply by changing the verbiage in the dialog box. There is no indication what the expression must equal, should it be "Show", should it be "Hide", should it be True or False, and if so, True = what? Show it or Hide it?
The second option is the "toggle item". This is a list of ALL Objects on the report, with no real discernible sort order, grouping, or any logic that I can see.