This led to the established in 2005 of Regulation NMS which was intended to assure that investors receive the best (NBBO) price executions for their orders by encouraging competition in the market.
[3][4] The focus on best execution by regulators has been blamed for unintended consequences, including the rise of high-frequency trading.
Under a Brownian motion with a high volatility, an instantaneous snapshot of the price process may not be a stable benchmark at all.
VWAP and TWAP are more stable as they are averaged over the execution horizons, but they are somewhat "flying" targets as the market progressively rolls out.
For most OTC products (e.g., non-listed derivatives), the single-dealer or multi-dealer platforms also provide access to principal liquidity sources offered by broker-dealers.