What's the point of adding a hashtag? When people on twitter add a number sign next to any letters (nospaces)it becomes a link. And if enough people do it, it can become a trending topic that twitter will list on the right hand corner of their main page for everyone who logs into twitter to see.
If you were to go onto twitter and see a #ww hashtag if once clicked, all the other hashtags for that particular link (#ww) will appear on your page. Depending on your browser power you could also see the following hashtags as people write them.