Must use this if you will wear face-makeup that day

Author's Rating:

Pros: great pre-makeup step: simple. no tints, crazy ingredients, or perfume

Cons: a bit expensive, but i haven't found anything better for less $

The Bottom Line: 
you might not have to wear primer if you have great skin, but i need it and found LC's to be the best for the price

Author's Review
before i tried it, i heard a lot about primers and specifically, accolades for the laura mercier one.  i thought... right, another gimmick from the comestic industry- trying to take another $30 from you for nothing. (kinda reminds me of that joke about the Frenchmen in the 80s who had an ingenius plan to bottle water and SELL IT for money).
well, i got a little sample of primer (from another brand) and was so shocked at how well the makeup went on top of it! (that other brand is very expensive so i never bought it.)   although you couldn't "see" it, all the bumps, dents, whatevers were filled in and smoothed out.  so when the makeup went ontop, it was also smooth!  primer really does set the makeup and make it last longer.
(the test: on days when i've worn makeup without the primer- at the end of the evening when i take my makeup off- i'll wipe as usual but notice there is significantly less makeup on the cotton pads.  you can only imagine where the makeup went. also, my face feels like crap at the end of the day if i don't wear primer... maybe it's mental, but it feels like all the makeup soaked into my skin.)
so we've established primer is good- but why laura mercier? well, i tried a lot of different primers, but found the LC to be the best.  it's less greasy and lighter than the other ones.  (if the primer is too greasy and you have oily skin, that could make your makeup melt even faster!)  the LC one is clear, where some of the other ones had a weird tint (either yellow or pearl- some people like that, but it made me look like a ghost.)  and LC is ok for my sensitive skin. 
personally, i like that LC doesn't have a strong spf (as many primers do).  if you want spf, LC make a tint with 20spf (in great shades!!).