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.

ClaytonL

Hate duplicate content? Hate wasting server resources?
Replytocom Controller gives you the option to remove “?replytocom” from comment urls and optionally redirect visitors & bots who try to use it anyway to a destination of your choice.
For those concerned about duplicate content for SEO purposes, the benefits should be obvious.
If you want to speed up your WordPress server, the redirection will let you stop wasting resources serving up the same page over and over again to a crawler bot. Even worse, pages with a question mark in the url aren’t typically cached by caching plugins like WP Super Cache. That means that those bot crawls are eating up way more resources then a normal url would. Now you can send them to a cached copy of that page, a less resource intensive page, or any other url.
Of course, the cost of all this is that visitors can’t have JavaScript turned off if they want to leave replies in threaded comments.
Borrows code from: 
* https://wordpress.org/extend/plugins/all-in-one-seo-pack/ 
* https://wordpress.org/extend/plugins/replytocom-redirector/

Replytocom Controller

Replytocom Controller lets remove "?replytocom" from comment reply urls and redirect bots who try to use it anyway.

Magic robots.txt vs Replytocom Controller