The biggest gift you can give to any partner in any relationship is your vulnerability. This can be your vulnerability during a scene, emotionally, or any other way to gift your vulnerability to your partner. In The Ethical Slutm, Dossie Easton and Catherin A. Liszt write that "Intimacy is based on shared vulnerability…nothing deepens intimacy like the experiences that we share when we feel flayed, with our skins off, scared and vulnerable, and our partner is there with us, willing to share in the scary stuff". It's not just about the submissive being vulnerable, but a shared vulnerability.
In my very humble opinion, it is imperative that an s-type see a D-type vulnerable as well. This will show the s-type that it's okay to show feelings of positive emotions and vulnerability. The most connected intimacy of a partnership is definitely based upon that shared vulnerability. Without that, does the relationship really deepen and grow? Does the relationship thrive? Does the relationship really have a deeper meaning beyond the surface of the connection? I, personally, do not think so. Positive emotions and vulnerability have to be displayed and accepted on all sides of any relationship in order for the deep intimacy of a relationship to thrive and grow.