Why add the site name to all headings?

Question

Search Engine Optimization

Often you will see the site title added to all page titles. More often at the end through a dash, slash or other character. For example, here on the toaster at the end through a dash, on habré and giktimes through a slash. Is it worth it to do so? Is there any seo sense in this and what? Is it possible to use not a word, but one letter or symbol as a site name?

Answer 1

Costs.

Answer 2

Is it possible to use not a word, but one letter or symbol as a site name?

And the meaning, one symbol of the role will not play and is not sought.
I think it's not worth it, because. it only makes sense for some branded pieces. For example, "Nashniki citylink", etc.

Answer 3

Uniqueization of the title, no more, because there is a chance that when inventing a title, repeat someone else's, and adding the name of the company or phone number nullifies this possibility.