The short answer
Do not stop at clicks or leads. Connect the same definitions from discovery through conversion, support, retention, and contribution margin before deciding whether to scale a channel.
Clicks and lead volume can make an unprofitable channel look successful. Measure the commercial path instead: discovery, trust, inquiry or product page, consultation or purchase, support, repeat purchase, and contribution margin.
Medical beauty requires inquiry, consultation, booking, visit, treatment, cancellation, and aftercare definitions. Consumer brands require product view, cart, discount, purchase, return, and repeat purchase. The decisive pre-revenue event changes by sector.
Every metric needs a definition, data source, owner, and review frequency. If a general inquiry and a sales-qualified consultation share one label, acquisition cost will be understated.
Review continue, warning, and stop thresholds before discussing scale. Leading indicators can reveal the blocked edge of the path before revenue has fully matured.