By default, the compiler uses shortcut boolean evaluation, i.e., the evaluation of a boolean expression is stopped once the result of the total expression is known with certainty. The {$B } switch can be used to change this behavior: if its argument is +, then the compiler will always evaluate all terms in the expression. If it is - (the default) then the compiler will only evaluate as many terms as are necessary to determine the result of the complete expression.
So, in the following example, the function Bofu, which has a boolean result, will never get called.
A consequence of this is that any additional actions that are done by Bofu are not executed. If compiled with {$B +}, then BoFu will be called anyway.