Here are the advantages:
1) Your hair will be in the best shape possible.
2) I can guarantee that you will be using a whole lot less in the way of conditioner.
3) Hair color dye technology has definitely come a very long way. Gone are the days of yesteryear when "hair dye in a bottle" was all one uniform shade. Even with a multi tonal formula, nothing works as well as what your DNA has given you.
4) You won't have to worry over whether your hair color will work with your color palette, because it will.
5) Less direct exposure to chemicals.
All of these things are good....but not everyone is ready for their natural hair color.
Maybe you are going or have gone prematurely gray.
If your hair lacks natural body, highlights do indeed add volume and lift.
Some women do not like their "mousey" hair and wish to enhance it by giving it more dimension and shine. (I say, try out your color palette first.....it may indeed change your mind about the whole thing.)
Is there anything wrong with giving your hair a kick of color? Nope.....certainly not! As a hair stylist, I really enjoy changing a client's look. It can be a whole lot of fun! Some of you might be looking for a drastic change. As long as your complexion can handle it....go for it.
I have to say, in my own case, my untouched hair feels nice and soft. It has a natural shine that no amount of serums or product can replicate. I don't have to wear as much in the way of cosmetics. Furthermore, the cosmetics colors I do wear tend to look better, because I don't have overly blonde or red hair fighting with my skin tone so much.
A nice added bonus are the the highlights the sun has given me. Instead of being brassy, they are the same tonal value as the rest of my hair. (Note the level of darkness in the back part of my hair....yes. It gets that light in the Florida sun just walking outside to my car. )
I have seen women go from hair tinted a dark brown make the transition into their natural silver gray and they look much younger rather than the other way around.
My suggestion is to give it a try. If it isn't for you, it's not....but if you have had your correct color palette chosen it will be surprising how much better your natural hair color will look!