Professional carpet cleaning- questions?

okay we are getting our carpet cleaned professionally. For about 50.00 more we can add deodorizer and stain protection to our order. My question is, does this really make a difference? do we really need it? We have a dog but he doesn't make a mess or anything. Won't just having the carpets cleaned deodorize them? Is this something we should spend the extra for or does it not really make a difference. Please let me know your thoughts and experiences. We are using Sears, they have the best prices.