Conversion tracking is - how is the campaign converting from one stage to another? Campaign stages usually are:

Conversion is usually shaped like a funnel image

Todays conversion tracking tools are pretty good - Our conversion tracking services matter when the campaign is paper based or multiple agencies are involved in running the campaign, or multiple tracking tools are used and the backend is named different:

This results in a situation like:

In such a situation, how do you really know what is the conversion at each stage?