I use pain in erotic spanking.
The main aspect of erotic spanking is clearly neither pain nor anticipation alone, but a combination of physical stimulation, emotional tension, and the psychological dynamics of power and trust.
However, when we look specifically at pain vs. anticipation, most people involved in erotic spanking often report that:
Anticipation plays a key role.
It is the tension, the thrill of control, the anticipation of the next stroke, or the emotional build-up that increases sensitivity and sexual desire.
For many, it is the anticipation or the pauses between strokes that are more exciting than the physical contact itself.
Pain is a means, not an end (usually).
In an erotic context, the pain is mild to moderate in intensity, often with elements of pleasant burning or heat that can be sexually stimulating.