Test suite is used to group test cases into one logical unit and executed as one unit.  Especially when the test cases are automated, running the TSER will in turn run all the TSER's for you.  If the order of the execution of the test cases within the module is important, you can control the order of the TSER's within the TSER when running sequentially.  There is also a roll-up verdict of the test suite execution result.

Now if the test cases within a test suite require manual testing and they can be run in parallel, then there is not much difference running a single TSER vs multiple TCER's.  It will be an advantage to be able to distribute the TCER's among multiple testers instead of assigning the TSER to a single tester.