Validating yourself will help you accept and better understand yourself, which leads to a stronger identity and better skills at managing intense emotions. Notice that mindfulness and self-validation go hand in hand.
At the same time avoiding emotions often results in quite negative consequences, while accepting allows emotions to pass and helps build resiliency.
Being present for yourself validates that you matter and that you have the strength to feel.
Being present with your internal experience means you experience the body sensations that are part of your emotional experience.
Validation means to express understanding and acceptance of another person's internal experience, whatever that might be. Validation builds relationships and helps ease upset feelings.
Knowing that you are understood and that your emotions and thoughts are accepted by others is powerful. Self-validation is accepting your own internal experience, your thoughts and feelings.
Self-validation doesn't mean that you believe your thoughts or think your feelings are justified.
There are many times that you will have thoughts that surprise you or that don't reflect your values or what you know is true.
You will also have feelings that you know aren't justfied.
If you fight the thoughts and feelings, or judge yourself for having them, then you increase your emotional upset.