Stonesetting is the craft concerned with attaching gemstones to jewellery. The stonesetter deforms the metal of the jewel in such a way that it holds the stone.
As stonesetting is a manual craft, the skill of the craftsperson influences the quality of the work heavily. This epresses itself both on the aesthetic level and on the technical level. In simple terms, a jewel should both be beautiful and well made.
Many people think that stones are set with glue. This is generally not the case.
Short answer: the microscope allows better quality control.
A jewel made by skilled artisans will please you for many years, even decades. In the current era of mass-production, it is often someone’s only possession still to be made by hand, to their exact requirement. If you want to enjoy your prized property for its full lifetime, it is important to return it to the workshop for cleaning and maintenance.