One view of the circuit breakers that Matt Levine just discussed this morning is that they help to avoid price drop due to liquidity issues. That is, algorithmic trading aside, many trades are still done by human beings who may not be paying rapt attention when a crash happens. The 15-minute pause gives them time to find out that something is up, at which point they may choose to start buying at the depressed prices, which will stabilize things. This also makes sense with the fact that the L1 and L2 breakers only trigger once each, once an L2 breaker has triggered everyone will probably be paying close attention to what's going on traders simply not being at their desks will become less of an issue.