Additionally, the user or arber is not interested in holding $1.00 in RUNE, they wish to swap to $1.00 in a non-rune asset - perhaps another stable. For THOR.BTC this asset would be L1 BTC. Here another slip-fee is paid. For USD since they have a choice of the median bucket, they will swap to the cheapest stable in the bucket, arbing that stable back to the $1.00 peg; as they collect a discount in the process.