While traffic is indeed a critical factor, it's the wrong one to focus on if you haven't invested in optimizing conversion on your web site.
Like George Kastanza figuring out a witty retort hours too late to use it, here I am some years later to present some pretty compelling math on why companies should focus first on conversion.
First, a couple assumptions:
- - The company in this example is selling a product (but the same principles work for ad revenues, B2B lead generation, etc.)
- - The company has not undergone extensive marketing optimization on their web site and/or promotions already.
- - There exists an opportunity to raise overall conversion rates by 5% or more (I have yet to work with a company where this is not possible).

On the other hand, if the company takes the time to run some insightful a/b tests on the ad and the landing page, all of a sudden the campaign is making money (ads and landing pages present significant opportunities for conversion improvement). Best of all, the campaign is now scalable. In this case, the logical thing to do is to NOW increase the reach of the campaign until it hits a point of diminishing return.
In the second example, let's have a look at web site conversion and the case for optimization versus spending on reach.

That argument would be true for the first month, but to truly understand the power of optimization, let's look at the math over a year:
- - Buying 10% additional reach costs $50,000 per month, which equals $600,000 per year, for a 160% overall ROI in the example shown.
- - Paying a consultant or agency $10,000 a month for 4 months is a good guess for what it might take to get 5% better conversion on a site with these kind of revenues (hey, I never said this blog wouldn't be self-serving sometimes). This assumes the site hasn't already been optimized.
In this case, let's assume the 5% improvement kicks in 2 months into the process. What this math works out to is that a mere $40,000 spent on conversion will result in $400,000 in new revenues for a 10x or 1000% ROI.

BTW, despite my tongue in cheek reference to hiring a consultant or agency, conversion and marketing optimization is definitely an area where you should develop in-house skills if at all possible.