When you need to have a Yes or No Parameters enabled by other parameters in your family. Usually you use ‘If’ statements to apply conditions…. Like shown below….
= if (Area > 1m²)
In the Case of a Yes/No Parameter, you aren’t required to write the ‘if’ part of the formula or the brackets. Just make the statement and Revit will do the rest.
The Example below has 2 sets of formulas both normally would be written with an ‘if’ statement, but in the case of a Yes/No, they are written without. (The top one is an ‘and’ statement requiring both variables to be true for the Yes/No to work.