The snap rule says that if a cash recall takes longer than a finger snap to initiate, liquidity could be an issue. Liquidity issues put your principal at risk in shifting markets. The rule saves you from asset price declines that significantly outweigh the income received from the asset. $10K in interest from a bond ETF that has declined $100K in value is not an effective investment, as it takes ten payment periods to recapture the lost asset value.
