I think there is. In the second case if there is work affecting common property, and things like waterproofing and plumbing, you need to make it clear that those works are the responsibility of the owner, not the owners corporation.
I would be very concerned if owners could do works and then if things go wrong with those works the OC had to foot the bill to fix them. Without a by-law how do you do that, bearing in mind that you need to bind future owners? (you can do a universal by-law that binds people who do works but that is another story)