The testsuite tag allows you to define testsuites under which all testscript tags are executed and monitored from the testsuite's perspective. The testsuite can be instructed to fail on the first error or to continueOnFailure by default, by continuing you can run through the whole testsuite and identify the testscases that are failing in a suite.
Testsuite tag will generate results that can be recorded by the Result tag this tag has the ability to record Testsuite and Testcase results to a different format that can later be processed and identify exactly where all the errors occured during testing.
Aside from being easier to read the end reports generated from the Results file it is also more convenient for keeping history of test results in this manner.