This is a question I've been asked a few times this year, especially since Lana (above) has been working with me, so I will tell you what I told those people:
To be honest for most weddings (less than 200 guests) I wouldn't say that you need to have a second photographer/"second shooter".
If it's something that is going to be an extra cost, and if it would make a huge difference to the overall price I would seriously suggest you think about it. It would be a lovely added bonus but it's not really a requirement. I cannot deny that having a second Photographer there gives you an obvious second person perspective and I can only be in one place at one time, but one wedding photographer alone should give you hundreds of images of your wedding day.
Often (like Lana) the second shooter will be there to purely get work experience and to shadow the main Photographer to learn and assist, and so they will often be there for free or for a very small amount. The reality is if they want to become a Wedding Photographer, experience is invaluable but difficult to come by. Unless they know lots of people getting married, it really is the best way to learn!
I hope you found this helpful and happy wedding planning!
If you have any questions you'd like me to answer, feel free to get in touch.
Love & stuff