If you plan on having many visitors to your blog, then you should definitely enable search on your website. If your blogging platform does not offer this feature by default, you may want to add a widget that will be able to do so. You can add such a search option by registering yourself at Technorati and claiming your blog there. I think that allowing search on your blog is especially important if your blog has many posts and otherwise it would be difficult for your readers to find specific articles. Adding various categories may help your readers to find relevant articles; however, the best way to find a specific post is by using a search tool.