A one shot exponential decay LFO is basically like an AD envelope. How fast or how slow the LFO rate is is basically like the decay time.
Try putting it on something obvious so you can hear what it’s doing, like pitch. If you put it on the pitch of a sample or, say, kick drum, you will hear it sweep from a point high above the base pitch down to the base pitch pretty quickly (like an envelope). An inverted exponential LFO would of course do the opposite 
One of my favorite tricks on the OT is to send an inverted exponential one-shot LFO to the rate of the sample, so every time the sample is triggered it sounds like a tape starting up.
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