The cash impact is a measure that shows success in the market monetarily using your RevPASH index. If this last one is 100 or above, your cash impact will be positive but if it is below 100, your cash impact will be negative.
For example, if your RevPASH index is 110 and your cash impact is £2,500, this means you have taken 2.5k away from your competitors.
But is your RevPASH index is 95 and your cash impact is -£700, this means your competitors have taken £700 from you.