I build cabinetry and prior to getting my Kreg I used a mix of T&G, dowels, and biscuits to join boards and frames together.  For your basic furniture construction this device is simply amazing.  Attach the jig to one face to be joined, run the special drill bit (included) down one or both fixed metal ferules, unclamp and use the Kreg screws to attach the two parts.  I can now build furniture, test for fit in the shop, take it apart, apply finish and rebuild on site.