The reason why you should soak weed wacker string is to help the weed wacker string become softer and less brittle.
Soaking the weed wacker string works well with nylon weed wacker string which most weed wacker string is.
When soaking your weed wacker string or trimmer string in water you soak the weed wacker string or trimmer string in water for at least 24 hours which helps to make it last longer.
I've been soaking my weed wacker string and or trimmer string in water before storing it and it has actually lasted longer than it would if I hadn't soaked it.
If you use the weed wacker string up pretty quick then you don't need to soak the weed wacker strong or trimmer string but if you buy the weed wacker string or trimmer string in bulk or in large rolls it's certainly a good idea to soak the weed wacker string or trimmer string in water for 24 hours to help make it softer and less brittle.