One of Laura Mercier product bestsellers are their primers. Their primers help the face get ready for foundation and enable the makeup to last long.
I've been using their primer too, and I only use little amounts and I'm still not finished with my tube. I like the cool feeling it leaves my skin and how light it feels (Sean Stevenson tip: Chill it in the fridge).
The primer comes in 3 kinds:
1. regular foundation primer
2. the hydrating primer - for dry skin
3. the oil-free primer - for oily skin. this one has a mattifying finish.
Primers can be used if you want your makeup to last longer, especially if you're attending a party where you wouldn't want to fuss much about makeup and would just like to have fun.