property OnlyWhenIdle: Boolean;

OnlyWhenIdle is a Boolean property that indicates when TIdAntiFreezeBase should yield when the Application main thread is idle. Set OnlyWhenIdle to True to prevent the component from yielding when the application main thread is not idle in DoProcess. Set OnlyWhenIdle to False to allow the component to yield when ShouldUse is True. 

The default value for OnlyWhenIdle is ID_Default_TIdAntiFreezeBase_OnlyWhenIdle, as assigned during VCL component streaming and in the Create constructor.