Analytics

It's becoming more important because the technology is finally available on a massive scale and companies large and small are finally realising the value of analytics.  Analytics helps you figure out the following:
Who's buying/using your product? If you know your audience well, you can tailor messaging, features, and business development to fit their needs.

What works for your business? Certain channels will work better at driving revenue than others for any business.  Knowing which channels work for your product can help you decide where to focus marketing and sales efforts.

How are your marketing campaigns actually doing? The days of reach and impressions as KPIs are long gone.  Now, online especially, you can get data all the way from the impression to the sale and use this information to streamline the purchase funnel as much as possible for users, incrementally driving up revenue in the process.

Testing! Your potential customers may respond much more to certain imagery, message, or even colours.  If your purchase funnel is exclusively online, you can test variations of each of the steps to turn the most site visitors into sales.  Well, run tests can have a huge positive impact on a business.  If you were to run tests on 5 points in your funnel and get an additional 15% performance out of each step, you would DOUBLE your revenue.

These are just a few of the areas that analytics can improve within a business.
Here's an example of a small business trying to advertise with and without a basic level of analytics:

Without Analytics
Bob owns an ice cream store.  Bob decides to buy a series of radio ads for $5,000.  Bob sees sales increase by $10,000 over previous months and thus decides, this is an acceptable return on the investment and continues to purchase radio ads.  Bob has no way of knowing if that increase in sales is because of those ads, seasonality, or any other contributing factor, so they may or may not be helping his business.

With Analytics
Bob decides to run radio ads with a radio-specific discount code for each radio station, $2,500 on a country station and $2,500 on a '90s station.  Bob tracks the use of each discount code over the course of the campaign and finds that the country station's code generated $1,000 in revenue, while the '90s station generated $9,000 in revenue.  Now that Bob knows that the '90s station grants a much better ROI for his business, he can choose to either invest the full $5,000 in the '90s station or even test a different media entirely, ultimately driving much more value to his business than if he weren't tracking the results.

In marketing and sales, and even business altogether, knowledge is power.  Analytics is all about knowing as much as you can about your own business to the point where you can materially improve it.