Keep in mind that it will all you to do either a Full or Delta inventory based on which options you select. aka the Delta is the same as click Hardware Inventory Cycle on the end client. The Full (aka prompted message) is the same as the delta but we first clean out existing HW details.

Then may be the name should be adapt to reflect that aspect?!

It reset the HW inventory so that you get a full inventory and triggers the HW inventory to run.

So full Hardware Inventory is doing what exactly?

This feature already existing within the RCT. Under Client action | Hardware Inventory, click yes to running full HW inventory.