Depending on the niche you're targeting, the FB Like buttons can either provide marketing value or just be a useless friction point in the UX.
You have to take a realistic look at if your content segment is something that people would actually do a Facebook like on. Having the like button turns out to be extra clutter in your user experience in many cases. For example, if your site deals with medical issues, it's unlikely many people will be "liking" that content (and have it appear on their feeds to friends).
Here are the benefits if your content is "like-able":
Exposure in friend feed
When a visitor Likes a webpage, the action is visible to all the friends of that person.
Viral marketing effect
People like to check out something that their friend has liked. A Facebook like is pretty much digital word of mouth marketing.
It all depends on the niche you're targeting and the "like-ability" of that content.
In many of my sites that target a B2B audience, we don't include the FB like button as it takes more away from the UX than it adds in marketing value.