One of the most frustrating components of traditional marketing is the inability to track results.
Unless you polled every single customer as to whether or not he or she noticed a particular ad, there's really no way to gauge its effectiveness. All you could do was measure sales numbers before and after you launched a marketing campaign, which is an inexact science to say the least.
Insert online marketing.
Digital advertising has been a breath of fresh air for companies for a number of reasons, as it's generally cheaper and can reach a wider audience.
But perhaps the biggest advantage of online marketing is your ability to track everything - conversions, click rates, follow-up actions and more. You never have to just assume a campaign's effectiveness anymore based on loose statistical relationships.