Lawyers can and will send cease and desist letters to people whether or not there is any legal basis for it. Often the threat of a lawsuit, even a meritless one, is enough to keep people quiet.

FYI, a "cease and desist" carries the same legal weight as me sending a one-liner saying "Knock it off".

They are strongly worded requests from a legal point of view. The only real message they send is that the sender is serious enough about the issue to have involved a lawyer, unless of course you write it yourself, which is something that literally anyone can do.

If you want to actually force an action, you need a court order of some type.

NB for the actual lawyers: I'm oversimplifying, since they can be used in court to prove that you tried to get the other party to stop, and tried to resolve the issue outside of court.