Difference between「行ってきます」and 「行って帰ってくる」


On [this page](http://www.dokidoki.ne.jp/home2/doinaka/iq/iq-h/i004.html)
about Imabari dialect, it says the following:

>
> 笑い話によく登場する話としては「行ってこうわい」。今治では「行ってきます」という意味ですが、他の地域では「行って帰ってくる」という意味に取られます。「行ってこうわい」というからずっと待ってたのに来なかった、というのがオチです。

I am not too concerned about the dialect itself, but rather the fact that the
above seems to imply 「行ってきます」and 「行って帰ってくる」have different meanings. (I don't
think difference in polite form is relevant so I will ignore that)

I was fairly certain that 「行ってきます」 on its own means that someone would go and
come back, however if so then it would mean the same thing as 「行って帰ってくる」. By
the way, I have never seen this latter expression before, not sure if it is
used often in everyday Japanese.




Even though they mean the same thing, 行ってきます has a much greater usage when
referring to going and coming back. When I have been in Japan, I have never
heard an individual use 行って帰ってくる when leaving, but instead 行ってきます.

