We use callrail to track calls from our programmatic media buys. It helps us track which sources are generating phone calls. In addition to the on-site conversions we see through the ad networks (Google/Bing/FB, etc.) it gives us visibility into the entire picture of conversions. This is critical because some sources generate more phone calls than others, and without a means to track/attribute where those calls are coming from it's impossible to optimize spend. So, seeing the whole picture of conversions enables us to optimize our media spend and get the most for our money.