Do we need foundation primers?

Haven't you ever wondered why are foundation primer necessary? How does a primer actually help the foundation and why do we need the extra step in our routine? Recently, I've started observing the primers I use own, as I really wanted to find out if they are working. I am actually proud of myself, as I only own three primers!

Let's start with the moisturiser+primer in 1, Smashbox Photo Finish Primerizer. At first, I really did enjoy using the Smashbox Primer during the colder months (I tend to wear heavier foundation in winter), as it's very watery and it works really well with heavier foundation, which requires a smooth/wet base. The moisturiser+primer concept is quite interesting, as it allows you to skip the moisturizer application step, the texture is also very lightweight and feels quite refreshing on the skin too.
- Helps to blend your foundation very smoothly.
- Acts as a moisturizer.
- Lightweight texture.
- Does not help your foundation to last longer.
Do we need it: No, unless you like to have a wet base before applying your foundation, but if you would like your foundation to last longer, it's not a primer for you.

YSL All Hours Primer is actually one of my favorite primer so far, if I need my foundation to last longer this is the one! I have noticed, that this primer tends to rub off if you are using a wet beauty blender to apply your foundation, so would reccomend to use fingers or brush to apply foudation. Stick to thicker formula foundation, whenever you are using the All Hours Primer.
- Helps to improve the wear and hold of foundation.
- Smooths out your complexion, perfect for minimizing fine lines.
- Contains SPF 20.
- It won't work with every foundation.
- Quite runny texture.
Do we need it: Yes, it's one of my favorite primers for a night out and would strongly recommend it. It's annoying that it does not work with every foundation, but I still adore it.

Guerlain 'Météorites'' Skin Perfecting Base won my heart purely beacause of the beautiful bottle! Yes, I love nice packaging and glass make-up bottles. However, apart from only having nice scent, I don't feel like the Météorites' Skin Perfecting Base is doing anything good. The watery/gel texture is very nice and refreshing. The primer contains a diamond powder encapsulated in microspheres, to create soft focus perfecting halo. You will notice a subtle illuminating effect on your skin, but I really haven't noticed any illumination/shimmer after applying foundation.
- Nice scent. 
- Anti-dullness make up base.
- Lightweight texture.
-Does not help the foundation to last longer.
Do we need it: Yes and No, if you would like something to look beautiful on your dressing table then it's a yes, but if you want a primer that works then it's a no.

In general, I find it really hard to judge whether we need primers or not. I feel like some foundation primers do work and are worth trying out, but some are just an unnecessary step in our routine. Honestly, some foundation will look amazing on top of a moisturizer and some do require a smoother base. What is your opinion on primers, do you use them?