In the ViewModelEditor, when selecting a ViewModelColumn, you see this:

The FollowEnable (Follow Enable) checkbox is there to reduce the need to write a VisibleExpression in the common case that you want your VisibleExpression to be a Negation of the ReadOnlyExpression.

Example:

ReadOnlyExpression: self.ThisShouldBeReadOnlyAndInvisible

You would then also need a VisibleExpression of : not self.ThisShouldBeReadOnlyAndInvisible

Instead of filling the VisibleExpression, you simply click the FollowEnable box behind the VisibleExpression. This will use a negated ReadOnlyExpression as the VisibleExpression automatically and you do not need to maintain 2 expressions.

(The reasoning for calling it "follow enable" rather than "follow a negated readonly" is purely space conservative.)