Matt is correct about repulsion. Think of it in terms of tension in a racquet. High repulsion can only occur when the shuttle contact with the string is low i.e. as soon as it touches the string, the string does its job. Low repulsion means the shuttle sinks into the string and more of its energy is absorbed. The strings, being a lesser tension, stretch more before catapulting the shuttle with the force of the hit.
If you’re not sure what tension to have in your racquet, then you’re in the same position as countless other players. This again is a very personal choice. It’s gets a little easier in time as your experience soon plays a part and tells you whether you prefer the string tighter or slacker. This means that even if you change racquets, you get quickly find your new preferred tension and continue enjoying this great game.
I’d say a high percentage of players haven’t got a clue about string or tension and probably don’t even care.
Paul