canons etc

[Alan J.Birney]

I am fascinated by the thread on canons and canon retaining 
headstocks and I am sorry that I dont have more to offer, but a 
couple of posts got me thinking.
On most of (if not all) the Italian bells (including modern bells)I 
have seen via the internet, canons are present.
Are these for decoration, or is there some advantage to having them 
that we are missing?
And what of button top (or flange top bells)- what was the purpose 
of these?

Alan