Why do people do this on Twitter?

[Oh My Gosh!]

Like they do this when they update:
#Example
WTF?

[Brainstormpc]

According to the official source:

Hashtags are a community-driven convention for adding additional context and metadata to your tweets. They’re like tags on Flickr, only added inline to your post. You create a hashtag simply by prefixing a word with a hash symbol: #hashtag.

Because Twitter provided no easy way to group tweets or add extra data, the Twitter community came up with their own way: hashtags. A hashtag is similar to other web tags- it helps add tweets to a category. Hashtags have the 'hash' or 'pound' symbol (#) preceding the tag, like so: #traffic, #followfriday, #hashtag. Hashtags can occur anywhere in the tweet: some people just add a # before a word they're using