Canonical URLs Explained

[Errol]

If i enable Multi-Field Plugin i get canonical url with the country location example below:
<link rel="canonical" href="https://www.my-url.com/united-states/classifieds/cellphones-tablets/phones/new-galaxy-s6-edge-4170.html" />


Why do we make the above url canonical instead of the url with out the country (base url) example below
<link rel="canonical" href="https://www.my-url.com/classifieds/cellphones-tablets/phones/new-galaxy-s6-edge-4170.html" />

1. Say i decide in the future to disable Multi-Field Plugin wouldn't this have a great impact on the current canonical urls with country name??
2. I would really like to know which is better for long term SEO.