Its especially useful to be able to threaten people with an audit when the tax code has become so complicated that compliance is nearly impossible.

For example, if a president nominated a certain person for a position that you happened not to like, it would be right handy if you were guaranteed to be able to prove that they "broke the law" when it came to filing their taxes if you looked hard enough. You could get a lot of miles out of that one before people realized it works on everyone.