Increase Defence buff is one of the ways in Raid Shadow Legends to help your team stay alive. Defence mitigates some of the damage you take from all enemies hits. A champion with a 60% or 30% Increase Defence buff will take their current active defence number including their gear and any active auras/enhancements and multiply that defence number by 1.6 or 1.3 depending on the strength of the buff. Some champions have their damage based on defence as well, this buff will enhance their damage output.