It’s a good thing to give user several ways to get to same point. Especially links to pages that you want people to visit, or pages that people are likely to look for. For example, you have one link to your “Our Product” page at the head navigation bar, and you have another link in the footer, and one other as a banner at the side of the page.
Same thing goes to search box. You can put your search box at the top corner of the page and put another one at the bottom. Just like what Google do. The point is we help user to go where they want to be in the quickest way possible.
Most users are impatience. They will go away if they don’t find what they’re looking for after three clicks.