Test suites help manage the complexity of the test implementation. Many system test efforts fail because testers get lost in the minutia of all of the detailed tests, and struggle to organize work and communicate results at an appropriate level of detail. Much like UML packages, test suites provide a hierarchy of encapsulating containers to help manage the test implementation. They collect tests together in related groups that can be planned, managed, and assessed in a meaningful way.

This might be one or more automated regression test suites, but a test suite can also be a work plan for implementing a set of related manual test scripts. Test suites can be nested hierarchically, so one test suite can contain others.

Consider creating test suites that arrange the available test scripts, in addition to other test suites, in many different combinations: the more variations you have, the more you'll increase coverage and the potential for finding errors. Give thought to a variety of test suites that will cover the breadth and depth of the target test items. Remember that a single test script (or test suite) may appear in many different test suites, so your tools should prevent unnecessarily repeated runs of the same test.

At a minimum, it's a good practice to start by organizing suites along the lines of major functional areas in the application. However, test suites might also relate directly to a subsystem or other system design element, or to requirements such as quality dimensions, standards compliance, and other requirements concerns that cut across the internal system elements. 

Some test automation tools provide the ability to automatically generate or assemble test suites.