This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
Tomcat only asks for them if you specifically set the APR connector in your server.xml file, otherwise it will use the pure Java BIO connector if the native libs do not exist.
Using the native libs essentially turns Tomcat into an A[ache Httpd server (quite literally) by leveraging the same code that an Apache Httpd server uses. You should se tremendous performance gains using this connector.