They want to see if your return matches the W2 and 1099 forms you got. And if it matches the copies they got from your employer and 1099 issuers. Or maybe your employer hasn't sent in their W2 copy yet. They want to make sure you didn't type in the wrong amount from your W2 or 1099. Or maybe you entered something on the wrong line. Could be a lot of reasons. There are probably people filling out fake tax returns and making up W2 entries to try to get refunds.
