How often do the Feds give "target letters," and why would they tip off a suspect this way?

Seems like a “target letter” is just a blatant tipoff to a suspect that he or she should flee or go into hiding. Unless…the idea is that the suspect is only being accused of a relatively minor crime, and hence is better off cooperating with the feds than running?

I assumed it was a means to tell the person under investigation that they cannot destroy any evidence.

Presumably, you can shred documents (as an example) as much as you like until told to stop. The target letter tells them to stop. If they continue to shred documents (or destroy other evidence) after getting such a letter they can be prosecuted for that.

A target letter informs a person who has been subpoenaed by a federal grand jury that they are a target of the investigation. Because grand jury testimony is compelled, the person is informed that they are a target in order to have the chance to secure counsel and understand their rights before testifying. A witness cannot have counsel present during grand jury testimony, but can assert the right not to incriminate oneself, and can ask to leave the room to consult with counsel before answering.

There’s a pretty good summary here:

(I’m not your lawyer, this is not legal advice).

This is really weird. I believe you that this is how it works but it is weird. You can’t have counsel with you but you can tell everyone to wait a while if you decide to go talk to counsel.

Seems dumb.