I've used it once, but I can't remember why.
Whatever company was using it, sent me a postcard with a barcode or something on it. It gave instructions for me to walk into any Canada Post and hand over my ID and the post card. The staff verified my ID and then scanned the barcode. I was then verified. It was quite a while ago, likely before most of the 'online ID verification' companies existed. I'm not sure how they compare in terms of cost, accuracy and compliance.