Guest Blogging/Posting Questions

Hi folks,

I'm studying (liking, actually) the idea of guest blogging or posting in some blogs
and other sites related to my topic. Some things have my curiosity meter up.

I notice some authors publish their articles elsewhere (i.e. Forbes). Then, they
put the exact same articles - word for word - on their own sites a week later.

Others do the reverse: they publish their articles on their blogs. They post the
same things, again word for word, on other sites after some time.

I'm rather intrigued why they did that, namely putting the exact same articles -
same titles, same content - on site A and then on site B after a week or so.
Two other things I notice is they don't link to where the articles have originally
shown, and they referenced instead where. (i.e. Cross post at X site.)

Does any of that have any SEO effect? Doesn't it make sense to first post your
article on your own site to establish authority before publishing it elsewhere?

I guess I'm also concerned of any backlash if I did that. But again, I'm intrigued
by what I observed.

Share your thoughts.