Gives you a benchmark for what you can spend to acquire them.
Since 1st Order
Look at the New Lead Cohort section of the Mission Control Dashboard
See when the value spikes up. That day is a milestone that you want to use for assessing your marketing campaigns. Note that paid media campaigns will react differently each time, and different than organic or legacy marketing activites that generated your past leads and customers. But this data point will give you a baseline for expectations of when to get concerned, if your paid media is not reaching the same value at the same time as your past performance.