Wordpress api key is very important for using the wordpress jetpack plugin. For hosted wordpress sites wordpress api key is very important. For protect your site from spam comments you need the askimet api key. which is common for jetpack and akismet plugin.
Spam comments are most irritating for bloggers. Reading the all comments and there content and deside. If Comment author URL is bigger then you should consider that comment as Spam comment for sure. Many times I observed, spammer always try to add there site URL in Author URL. Using following code you can protect your site from spam commenters. Open your functions.php file from your theme folder and just copy/paste the following code into that.