You can avoid damage through agility and “rolling” with an attack. You receive a bonus to your Toughness equal to your advantage rank, but it is considered an active defense similar to Dodge and Parry, so you lose this bonus whenever you are vulnerable or defenseless. Your total Toughness, including this advantage, is still limited by power level.
This advantage is common for heroes who lack either superhuman speed or toughness, relying on their agility and training to avoid harm.
D20 Hero SRD Advantages Article-http://www.d20herosrd.com/5-advantages