0.09 thickness is a unique lash extension thickness in the lash industry. However due to the very special thickness it is incredibly versatile and can be used for these types of looks. 

Ultra light and natural classic lash look when applying one lash to one natural lash

2D closed fans that mimic the look of flat lashes

2D open lash fans - to create light volume where 0.10 thickness would be seen as too heavy for natural lash. 

2D light wet look lashes that is current fashion where two lashes are picked up together to place on one natural lash.