"Just because UV gel nails look cured doesn't mean that they are properly cured.

Under cured UV gel nails will be prone to staining, lifting, breakage and your clients will be more at risk at developing product related allergies.  The dust and under cured product can also be a problem for the nail technician".  

Doug Schoon.

https://schoonscientific.com/wp-content/uploads/2016/08/article-7-Secrets-to-Curing.pdf