A. Volatility
Studies shows that GBP pairs are the most volatile in the markets. With an average daily range in price movements of 1000 to 1500 points (100-150+ pips)
B. Dollar Value Per Point
The dollar value per point on most USD pairs (majors) are often $1 per point per standard lot.
What this means is that when you open a USD pair position say GBPUSD with a standard lot, and you are willing to risk 250 points (Stop loss set at 25 pips) and you are projecting to target 1000 points in profits (take profit set at 100 pips) the dollar value for your trade is -$250 when it goes against your projection, +$1000 when it goes in your projection.
This simple trade gives you a risk to reward ratio of 1:4.