I use to think that. I'm capable of putting numbers in a form correctly. A good tax preparer can point out things like "did you know that your specific commuting pattern entitles you to claim mileage?", or "the law says the way you have your working environment set up at home means you can deduct some of your utility bills", and so on ad infinitum.

Basically, unless you get someone who has a deep knowledge of the law, if your tax situation is non-trivial (see my post above this) then you might be leaving money on the table. It's a terrible, idea to evade taxes. It's a fantastic idea to realize when you're paying more than you're legally required to so that you can fix it.