Chanel Foundation In General:
It's useful for me to talk about this before Le Blanc de Chanel to put things in context.
There are a few things that I don't mind spending a bit more money than usual on and Chanel foundation is one of them. I didn't actually use foundation until a couple of years ago as I don't have bad skin and always thought that you only really wore a proper foundation if your skin wasn't very good. But then one of my friends who was in love with her Chanel foundation jumped on me one night before we went out and suggested I try hers out. I loved the results! It made my skin look pretty flawless but not in a fake, too-made-up way, in a pretty natural way. You can get it in a number of different shades to suit your skin tone but you can also choose whether you want Pro-Lumiere which gives a slightly shimmery, glowing look and is nice in summer months, or a Chanel Mat Lumiere which isn't shiny at all. Because you can choose carefully what you go for it means that you can make sure you get the right match for your skin and there shouldn't be that orangey fake tan look and difference between your face and neck that you get with some foundations. It's not cheap though and at about £35 for a bottle which will probably last a few months, you may not want to use it every single day.

Chanel Le Blanc de Chanel:
I went for a free facial at the Chanel counter in John Lewis a few months ago. As usual the beautician used about 20 different products all which only seem to make such a tiny difference when used in isolation for quite a high price, but when you have the finished look you're often tempted to buy it all because they do a really good job. But of course if you bought everything it would be potentially a few hundred pounds so I followed her suggestion on what I should go for and this was one of them.

What you use it for:
You use this product before you put on your foundation to create a nice base for your foundation to go on. I didn't realise until then that this kind of product which you put on before your foundation to create a nice base is called a Primer. It feels lovely and soft and silky and I do find that it makes your foundation not only go on more smoothly and get a better coverage, but also keep the nice look for longer. The beautician used a brush to put it on and suggested I also do the same but I just use my fingers and put it on in exactly the same way as foundation and it works fine.

Tip:
You don't have to use it under foundation, you can wear it by itself for example in summer when your skin is looking good anyway or during the daytime for a more natural look. It brightens your skin up a bit and makes it look more flawless.

Cost:
At £27 in Boots for 30ml it isn't cheap so again you may not want to use it all the time - I just save it for when I'm going out.

Any Drawbacks?
Obviously the cost. I would also say that if you have a limited spend for make-up it probably shouldn't be one of the first things on your list as the results aren't dramatic, it is a bit of an extravagance.
One other thing I will say is be careful with the bottle and not to spill it, as firstly you'll be devastated if you waste it by tipping it on the floor, but also because it's white it stains carpets really badly!