Algorithus

This plugin allows you to easily control whether search engines are disallowed from accessing the root directory of your WordPress site by modifying the robots.txt file. You can enable or disable this functionality from the “Reading” settings page.

AWP Disallow Root Control

Disallow access to the root directory via robots.txt with an option to enable or disable.

ABCdatos

In a nutshell: You don’t want robots wasting your resources and slowing down your site if they don’t give you some kind of direct or indirect benefit. An optimal configuration will maximize your SEO results and reduce your operating costs.
You’ll need less than a minute to set your site characteristics and get a customized robots.txt configuration installed, matching your needs and easily updated without headaches. Let us to apply our experience in maintaining and optimizing sites. A clear knowledge of what we want to do and why, moved us to change the decission method from human created robots.txt to an automated system, things are simpler as they seems. Here comes to help this plugin, doing all the magic for you.
Some of your site specs will be automatically detected to reduce the manual config needs to the minimum. A few simple questions about your site will be enough to vast majority of sites.
<h3>Update procedure</h3>
Any change required to the robots.txt is applied in real time when operating in virtual file mode. If you are working in real file mode, after updating the plugin version you should click the Save Changes button in the configuration screen to regenerate the robots.txt file.

Magic robots.txt

This plugin automatically creates a robots.txt analyzing your site to improve your Google ranking and site performance.

AWP Disallow Root Control vs Magic robots.txt