Because data sufficiency questions are the most confusing for test takers, they're almost universally despised. I love them, though, for a very important reason:
They put my students into Harvard, Stanford and Wharton.
Most Test Takers are Wimps.
They don't want to work hard. They don't want to suffer through question types that they don't understand. And frankly, most GMAT instructors dislike data sufficiency too, so they do a bad job teaching it. As a consequence, most test takers perform poorly on these questions and create an opportunity for others to beat them.
I take advantage of that opportunity. My students and I spend an inordinate amount of time in class doing data sufficiency problems. We work on the highest-level concepts because we know that others will miss those questions.
Why is Data Sufficiency so Important?
Contrary to what the test writers say, the GMAT is graded on a curve. (It's pre-established by other test takers and then adjusted if necessary in the aftermath of your exam.) To beat an opponent on a curve-based test, you need to hit him where he's weak. That means data sufficiency. To ignore these questions is to forfeit your opportunity to pull ahead.
If you want to neglect something, neglect reading comp. Frankly, it's harder to improve in that section. Accept data sufficiency as the price you pay to go Wharton and study it every day. I guarantee you that it makes perfect sense and can be learned completely.