[gst-devel] what the meaning of GST_TYPE_PARANOID?

[Kang Jeong-Hee]

I've found gstpad.h #define GST_TYPE_PARANOID,
and other bin, element, object, pad.h refer like this:
"""
#define GST_OBJECT_CAST(obj)            ((GstObject*)(obj))
#define GST_OBJECT_CLASS_CAST(klass)    ((GstObjectClass*)(klass))

#ifdef GST_TYPE_PARANOID
# define GST_OBJECT(obj)                (G_TYPE_CHECK_INSTANCE_CAST ((obj), GST_TYPE_OBJECT, GstObject))
# define GST_OBJECT_CLASS(klass)        (G_TYPE_CHECK_CLASS_CAST ((klass), GST_TYPE_OBJECT, GstObjectClass))
#else
# define GST_OBJECT                     GST_OBJECT_CAST
# define GST_OBJECT_CLASS               GST_OBJECT_CLASS_CAST
#endif
"""

what is the meaning of GST_TYPE_PARANOID?
why not use just G_TYPE_... directly?