Cheap Rooms! You can share a room or stay in a private room right in the center of a beautiful city like Paris, London or even New York for a small fraction of the cost of a hotel room. Easily compare the costs of hostel vs hotel and you'll see the differences easily.
Many hostels offer charming, trendy accommodations with conveniences like WiFi, TV, internet cafes, book exchanges, bars, etc.
Local staff is usually very knowledgeable and able to give great advice on the best places to see, things to do, transportation, and places to eat. Many times you can also get great discounts on different attractions.
Communal style living where you can meet other travelers from all different places and walks of life. A great way to build new friendships that could last a lifetime.
Some hostels have eat in guest kitchens so that you can buy food at the local grocery and eat in to save money and not have to eat out at expensive restaurants every night.
Hostels offer a unique experience in a relaxed and laid back fun environment. Definitely a creative and inexpensive addition to make your trip even more memorable.