If a company has $100 million in equity value (equity provided by investments by owners and shareholders) and $400 million in enterprise value, it's the same deal -- the enterprise value includes the debt that's encumbering the business, too, and has to settle that up before being able to cash out.
Why does equity value matter?
Equity value tells a story about how much of the company is actually owned by owners and investors and how much is encumbered by debt and other obligations. Although you can easily look at debt by itself and examine the balance sheet for other obligations, you can also first simply look at equity value to see just how much equity there is by comparison to the enterprise value.
If a company has a lot of equity value compared to its enterprise value for its industry, you might be able to assume that it's pretty responsible, it's not getting in over its head with debt, and it can be counted on long-term. If it has a small amount of equity value and a lot of other obligations, it might be a bit more worrisome. Having a smaller percentage of encumbrance as a business generally means you can move faster, absorb larger unexpected economic blows, and continue to thrive in all kinds of business environments.