So this is a setting-spray or 'fixer', which is basically a spray that you use to keep your makeup from straying throughout the day. Personally I don't have problems with my makeup smudging or slipping but I can benefit from the fact that setting sprays are also intended to keep your makeup looking fresh and just-applied.
This particular fixer also claims to give your skin a fresh dewy glow, which is a look that I really love, however I know not everyone is about that. So if you're more into a totally matte finish, maybe give this one a miss.
On the note of possible down-sides; this is also - like almost all Etude products - is somewhat scented, so if you're prone to skin irritation this could be one to avoid.