Speed to lead is the elapsed time between an enquiry arriving and a human responding. It matters because buyers typically contact several suppliers at once and engage seriously with whoever replies first, making latency a competitive variable rather than an operational detail.
The foundational research (Oldroyd, MIT Sloan, 2007) found qualification odds dropped 21x moving from 5 to 30 minutes — old data, quoted with its date.
It is usually the cheapest available improvement in the entire funnel.
Measure it yourself by submitting your own form.