Planning Test Cycles and executing tests as part of those cycles is very powerful yet easy to set up.
Based on your Test Process, you could have a very simple flow where you could create and execute tests in an ad hoc manner, but if you have any basic execution planning in place or have a more elaborate structured test process, then planning your test execution ahead of time is important. Test Cycles are used to set up and execute tests in a structured manner. This allows tests to be grouped logically and executed in a structured fashion. It also allows for the tracking of progress and reporting of quality metrics.
The "Ad hoc" cycle is default in every version. If no version exists for the project, then it is listed as "Unscheduled", and will also have an "Ad hoc" cycle.
The progress tracking status bar provides a quick view on how many tests have been executed, what % of the overall testing has been completed for a test cycle and on hovering over the different status colors, the # and % of tests in that status (e.g. PASSED, FAILED etc.)
Clicking on any test cycle displays a list of tests for that cycle, which can then be executed or viewed. You can also expand the Test Cycle to view the folders in that cycle by clicking on the arrow located next to the cycle. Each folder can have its' own set of executions as part of the overall cycle.