Recently a high ranking us gov. official plead the 5th during a particularly complex trial that was part fishing expedition.
Now that I have more experience working in government, I realized I had a new interpretation of her actions that were not immediately 'she did it, but doesn't want to admit it'.
Every day officials are asked to make an awful lot of decisions, based on limited information. Some of them are no doubt corrupt, but many are trying to do the job to the best of their ability. But they are human, with biases and foibles and sometimes just plain oops moments.
In the case of this trial, it was high profile, and it was slanted just enough (as I recall) that the people on the other side of the table would have been very happy to find any misconduct, of any kind.
More than likely, at some point in her career, she did something that was not, strictly speaking, completely legal. I don't think it's possible to avoid it, given the size of the bureaucracy and the rules governing it.
In this case, the 'MAY incriminate me' becomes just that - 'I know what I did, and I did the best that I could, but frankly, maybe something in there wasn't strictly in line with every one of the 10.8 bajillion rules.'
This could (I'm not saying does in every case, but could) prevent some rabbit hole/witch hunt situation that just doesn't benefit anyone.