Most tax professionals are awesome, reliable, knowledgeable people. But as with many professions, there's always potential for running into a less than ethical "expert." The IRS routinely investigates people who profess to be pros (certified public accountants, enrolled agents, tax attorneys) but who really aren't. They falsify deductions, income or dependents in an effort to produce a larger refund for their clients and alter documents, among other offenses.
And apart from that, sharing your financial information with anyone, for any reason, carries some inherent risks. Even the most ethical, conscientious preparer can fall victim to a hack or break-in.
That's another reason why some of us prefer to handle tax returns on our own. It's possible that you could wind up making a tiny error or two, but my guess is you're not likely to try to embezzle your own money. So if you're the type who prefers to avoid potential drama, it might be best to file your tax returns from the comfort of your own computer, where you can keep your own eyes on your own money.
Just be sure it's a secure WiFi connection, or else it defeats the purpose, OK?