This is a complicated question, but i'll try to explain it as best i can.
BDSM is part of my lifestyle, as much, much more than sex. Relationship and lifestyle wise, my Mistress and i have a more-or-less 24x7 Mistress/girl (Dominant/submissive) relationship. Wwe have a list of protocols and rituals Wwe follow that are part of our daily lives. i have tasks to do and rules to follow and punishments, usually of a non-play, non-sexual nature, result from my failure to meet Her expectations and rules. Wwe incorporate BDSM play into Oour sex-life but, really, the bulk of the D/s in Oour relationship occurs outside the bedroom. Why? Because it makes us both happy. There are a lot of benefits. Oour relationship is structured with boundaries and expectations laid out, quite literally in black and white, on paper. She knows that things will get done the way she expects and needs them done (She has mild OCD) or She has every right to make me correct them and/or punish me. She has every right to demand that the bed get made, the dishes get done, the towels get hung, Her laundry gets folded and put away, all to her specifications. i have a tendency to be a bit on the messy side and not be the best homemaker so these things could easily be a point where Wwe butted heads or argued or had other issues if Wwe didn't have this structure. Wwe are both creatures of habit who are comforted by ritual. Having certain expectations and rituals in place helps Uus both feel comforted and really alleviates stress. It makes Uus both feel safe and loved and reassured. Another benefit to the structure of Oour relationship is that when something isn't working, Wwe have methods in place to deal with the problem, to negotiate changes within the structure of Oour relationship. All of Oour little protocols and rituals and rules serve as constant reminders of Oour commitment and care for one another. Even something as simple as me walking on Her right side at all times shows her that i am and reminds me to be ever mindful and attentive to Her. The necklace i wear at her bidding reminds us both of Oour relationship at all times and helps Uus feel connected. When i complete some task or obey some protocol, it's a way to show Her that i care and am thinking of Her. When She says "Good girl" it makes my heart swell like no other compliment anyone could give me. When She touches my neck and fingers the chain of the necklace, it gives me a feeling of pride and safety and security. Through these little things, Wwe wordlessly say "Ii care about Yyou" hundreds of times a day. Communication, constant, thorough, honest communication is VITAL for all of this to work. Wwe have a ritual in place to ensure that communication occurs regularly and in a way that facilitates growth and Oour mutual happiness and contentment. i'm capable of finding any and every part of this a sexual turn on, but it's about so much more. For Uus, this is the way to have a peaceful, happy, fulfilling relationship. It's not for everyone, but i don't think i would ever be in a non-D/s relationship ever again.
Wwe are also a part of the kink community and attend events and meetings which has led to meeting some of the most wonderful people and has caused Uus to make some lasting connections and learn and grow in ways neither of Uus could have imagined. For those drawn to this lifestyle, it truly is a beautiful and wonderful way to live and have relationships, both platonic and romantic. i literally cried tears of joy and relief the first time i attended a D/s support group meeting.
Also, i am inclined, by nature, to serve and please others. It is easy for me to find myself in relationships, romantic and otherwise, where i give so much that i may be taken advantage of because i continually seek to help others and to gain their approval. Being in a consensual, negotiated D/s relationship as a submissive to a caring Mistress provides me with a structured, safe environment where i can safely serve and give while trusting that i won't be taken advantage of and will receive the approval and appreciation i need from my Dominant. This leads to me being taken advantage of by others far less and being much more fulfilled and happy.
D/s also serves as an outlet to punish my failures in a way that i find acceptable. i'm the type to punish myself when i feel i have failed or messed up. However, if i am punished by my Mistress and deemed forgivable by Her, then i necessarily MUST forgive myself by nature of my submission to Her. This leads to me being plagued by far less guilt and self doubt and i am happier and healthier and less stressed.
For sex, submission is just simply a turn on for me. Punishment is part of my relationship and pain, whether as punishment or for pleasure, is a part of my life that i love and couldn't ever do without. Pain also serves the purpose of catharsis. It helps me deal with stress, anxiety, self-doubt, guilt, sadness, mourning, anger, and other negative emotions. It helps me to release them. It helps me to cry when i need to but i've been fighting back the tears for too long or too hard so that i can't let them fall anymore. It lets me have a much needed release that is hard to find otherwise. Pain turns me on, it makes me feel good, it relaxes me, it clears my mind, it lightens the load on my shoulders, and has very good psychological benefits for me.
The human body releases some pretty awesome natural pain relief responses too, which can equivocate a type of "high". I can feel loopy, giddy, silly, etc. In addition to the bodily chemical responses, i just feel lighter, my step feels springier, the weight on my shoulders is lifted, my spirits are higher, and i feel immeasurably more relaxed after a good scene.