One of my more common refrains is: If in doubt, follow the instructions, otherwise, yep, follow the instructions. Indeed, this is part of my signature in another forum.
I did not. But I deviated not by much. And only after carefully weighing as many factors as I could identify and doing some homework. It might be apparent, I have done a bit of homework.
Generally there has been no indication that including anything extra in the application has helped anyone. There have been many indications it failed to help.
My deviation was to include CRA Notices of Assessment. I am self-employed. After careful study I concluded that including the CRA NoAs would cause little or no risk of hurting my case. I cannot say it helped. I sailed through the process easily, taking the oath barely eight months after applying, back when the reported routine processing time line was well more than double that (app to Sydney July 2013, took oath March 2014). But others attending the same oath ceremony as I did also sailed through quickly, some in just six months.
Note regarding consultants:
IRCC recognizes and will deal with those who are authorized representatives. Frankly, I would not trust any "consultant" unless the consultant is in fact an authorized representative.
The sad side of this is that there are probably many genuine consultants with expertise and engaged in what they do to help. But there are way too many whose motives are not particularly honest let alone service-oriented.
On the question posed here, I too agree with the "consultant," but in general I'd suggest exercising some caution in dealing with consultants unless the consultant is a licensed lawyer or a formally authorized representative.