Have written letters for others.
Have written speeches for others.
Have written articles for others.
In most cases, under the originator’s direction and with the originator’s input, review and ultimate approval.
Performing such functions when someone has confidence in a particular writing style. The ideas remain his or hers. Never a question as to who sets the scene.
Whenever words are through another, there is a risk that the other considers that he or she has the power, while the originator is little more than a mouthpiece. Megaphone for the background puppet master.
Would meet the odd assistant on Parliament Hill who conducted himself or herself as if the assistant were the de facto Member of Parliament. Don’t know if the actual Member of Parliament appreciated how power had transferred, or was perceived to have transferred.