Why does the same Rule Calculating The Sell Price Of A Product fire multiple times?
This is because the price is calculated during preparation for display where the field is rendered on the page, for the Add to Cart form to determine product availability, and for recalculation of any instance of that product in your cart. I believe we tried caching calculated prices in the product entity at one point in time to avoid duplicate calculation, but that obviously didn't stick. I don't have a solid recommendation here, just wanted to provide the info requested. Also, note that cart price refreshing is adjustable but is intended to happen in realtime with the full cart context. I'd think you could safely find a way to eliminate the duplicate calculation between the price field and cart form, but you'd want to do it without interfering with the cart refresh.