Lots of marketing people classify prospective lead using an hunch. this happens due to the fact that there is an certain amount of trust/bond formed between the marketing person and the lead during the interaction.

Traditional ways of classifying a lead is Hot/Cold/Lost.

this does not tell much about prospective leads. nor is there any quantification of why is a lead hot/cold/lost.

The result of a lead scoring system is the ability to rank and prioritize opportunities. Equally important, it will allow you to send leads to the field using a system that is agreed to in advance and is quantitative. A sales organization receiving a lead with “52/65″ (meaning a score of 52 out of a possible 65) used to classify the lead, versus “Hot”, is much more in-tune with the pre-qualification process that has occurred.

numerical scoring helps companies in the long term due to the fact that they have clear idea why a “x” lead is much better than “y” lead.