Taking the battens out of the sail will harm it more than let it in, because the edge of the batten will chaff the sail where it is most vulnarable.
Since most battens and sails are of non-creeping materials, I don't see any benefit in releasing the tension. And tension the battens takes a lot of time which I want to spent on the water.
I am not aware that salt will harm a sail, other than moving the sail with sand/salt on it. And you have more movement, when you take the sail out of the snuffer.
In my opinion a sail last long, if it is protected from sun light, if you stuff, furl or fold it as less as possible, if you avoid flagging in the wind.

Cheers,

Klaus