I think the old version of emojis(like `:)` `:|` `:(` `:D` `:P`  ………)are more then enough for adding expressions to your text.

Also I don't really like emojis because on most mobile device the capacity of symbols is limited and therefor emojis often replace useful (math) symbols(like `¹` `²` `³` `⁴` `⁵` `⁶` `⁷` `⁸` `⁹` `⁰` `⁽` `⁾` `⁼` `⁺` `⁻` `₁` `₂` `₃` `₄` `₅` `₆` `₇` `₈` `₉` `₀` `₍` `₎` `₌` `₊` `₋` `∇`) I cannot write anymore.

And in general I think most of them are completely useless. Some people tend to place the emoji resembling a word behind the word(like "…cherry`cherry emoji`…").

Also I think as useful as they may be they can also lead to some confusion at the other end because most emoji look the same on first sight.
Also a problem is if the sender uses a wrong emoji or something.

So I would say they are no advantage.