I thought the post was in reference to a letter from employer about employment in Canadian office. If I misunderstood, that's my mistake and I apologize.I read it more in the context of an answer to the previous suggestion:
"Provide a written and signed statement from each of you about your intent and maybe posts/emails/texts to friends and family about moving."
To this I would indeed respond, no offense, that there is no point in having that as your plan to show Intent. Especially with the recent history of people not travelling (you can see multiple current topics on people needed extension after extension) the requirements are much stronger than just a letter and maybe some emails/texts.
With this big picture in mind, no point.
The letter would be kinda necessary though as part of the package sent. Your letter should tie to your specific plan, i.e. quote/reference the other documents you attach:
We plan to move to this city, see attached job search (2a) and appartment search (2b), school research (2c).... so on and so forth for each step of your plan. A letter copy pasted from a website as to your intent (I "Anonymous" Intend to move to Canada as soon as I receive PR. Signed, "Anonymous")is pretty pointless in my opinion, a well crafted letter that highlights and details your actual, specific and personal situation and plan would however make for a strong case provided it has all the necessary supporting documentation.
I agree a letter just stating I plan to return is not much use. Or perhaps can be included but without supporting evidence is not much use.