The definition of the Hashtag is to highlight key words in your tweets. If you click on a hashtagged word or phrase, it will bring you to a search results page with other tweets with the same hashtag. They can also be used to create conversations, or chats if you will.Hashtags must be used properly, at the end of a sentence with appropriate words or phrases related to the tweet.
So why do people still use them in the middle of a sentence? I have to admit that I have been guilty of this in the past, but one has to make mistakes in order to learn and become a better tweeter. Mid-tweet hashtags were used when the emphasis on using hashtags was most popular, but it's an old practice.Overusing the hashtag in order to create more coverage for your tweets may work, in theory, but the construction of your tweets may confuse your followers. Instead, cut down the use of your hashtags to one or two words or a phrase that is commonly used. You'll still get your message across without annoying anyone.
Let's not forget #useyourhashtagsattheendofyourtweet.