Why use the # sign in Twitter?

[Jacki Delso]

I understand it links to tweets talking about that word, for example
"Naps are good! Showered and fresh time to go out! #smellinggood"
Why would you randomly use # for smelling good, or for any words at all?
I don't understand the concept

[Fin York]

Its called a hashtag. When you click on it it shows all related tweets. Also it feeds into the twitter trend data.

People who use it like you suggest have missed the point.