I took your questions as a great opportunity to rethink. I've been practicing and teaching Validation for 10+ years. Sometimes I like to look back at what I've done, decide if it was a "good thing" or a "learning experience" and to refresh my views.
My belief is that discovering Validation was a Wholly/Holy Wonderful thingy.
But you asked why? So I thought for a while and came up with three answers – three benefits. Then I asked Sandra and she popped up with the other side of one of my three benefits. I'll be brief.
Reason #1: Safety.
If you live with another person your greatest risk is that they will keep critical secrets from you. You may be living in what I call a "Fact Void." Probably all of you who have lost a partnership have discovered this. It's what he/she wasn't saying and you weren't hearing that killed the relationship. The habit of Validation brings you face to face with what is going on inside your partner in a reliable trustworthy/trust building/trust maintaining way. The habit of Validation also makes for a reliable safe way for your partner to feel seen and not feel ignored – to speak up. Safety in relationship is created by the habit of Validation. That's my firm belief and my first reason.
Of course if you don't want safety in a relationship, skip learning Validation. That's my corollary.
Reason #2: Narcisism
In this culture I fear it is easy to develop narcissist habits. In the early part of my marriage, to make things simple, I think I was a "narcissist prick". Of course I learned these skills from my parents and the people around me, on TV, etc. I've learned that the future for all NPs is to live alone with everyone hating you – just a matter of time. Or you can learn to quit those habits. The prime missing element in NPs is their ability to be empathic. I firmly believe Validation is a specific skill to teach habits of Empathy and to remove the catastrophic habits/consequences of being NP.
Of course if you want to live alone, skip learning Validation and also skip learning Empathy. Just my thoughts.
Reason #3: Self-Esteem
A normal problem in raising kids or running relationships or, hell, the welfare state is the tragic lack of self-esteem in most everyone. Learning to have or build self-esteem, guiding people into self-esteem is I believe a direct result of the application of Validation. Teaching people that they don't have to be like you, also teaches them that they are responsible for their happiness and misery. They can make their choices. They cannot be victims. I've learned that any sane culture wants people to have high self-esteem because those people are more productive toward the culture. I've learned that if you have to build self-esteem in secrecy, then your productivity will tend to be simply rebellious and culture-negligent/destructive. I firmly believe that Validate builds self-esteem. That's my third reason.
Of course if you just want to stay a victim or just want people around you to be victims, skip learning Validation. Just my thoughts.