Validation is a communication skill to improve the relationship. In it's most effective state validation:
lets them know they are heard and understood
can create within them a more calm state
helps us to stay focused on being present in the moment w/out problem solving or becoming emotionally distraught
can lead to the opportunity to present validating questions which in turn keeps the problem solving responsibility with them where it belongs
when they come up with their own solutions they are empowered
The best resource for learning the art of validation I have found:
"I Don't Have To Make Everything All Better"Here is a workshop on validation to get you started while you wait for the book

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Communication: Validation Tools and Techniques