effectiveness of groups and free ad sites

this ia a moot uestion...very very relevant to any business .. What is the effectiveness of free ad sites ? are they usefulon gathering businessess? well the lure of more traffic drags one to all ad sites worth the name ..just in case one gets a single effective lead?..this expeectation is belied and is not commensurate with effort energgy and times spent.. as all want free stuff and ther are many tire kickers What is the truth? hahahahah lets debate and discuss? ok here we go