Page History

...

No. You can simple use the standard flat organization, right on the issue screen of the Test Plan where you can also rank the Tests the way you want. The Test Plan Board is something that you can choose whether to use or not, in each Test Plan, in order to organize hierarchicaly the Tests within it and track and manage the progress of subset of Tests. 

Are there any advantages of using the Board even if I don't want to use hierarchical test organization?

There are some that may be useful to you, including:

• ability to easily see the overall progress for all Tests, in a given Test Environment
• ability to easily filter out the Tests you want, for scheduling Test Executions