A disclaimer will not keep you from being sued, but it may keep you from losing the suit. While anyone can sue you for anything, an individual will have a much more difficult time proving you should be held legally liable for something that you had clearly posted a disclaimer about.
For example, say you run a blog where you share financial opinions and are talking positively about a specific stock one week. One of your readers invests his life savings in the stock you liked, and the stock crashes. The individual wants to sue you for giving bad information that led to his loss. But you have a clear, concise disclaimer on your site or in your posts that makes it clear you're only sharing an opinion, are not giving professional advice, and you are not to be held liable for any financial losses anyone experiences as a result of reading your opinions and acting upon them. Even if you do get sued, the court would likely rule in your favor since your disclaimer made it clear you were not giving professional advice.