This item was looted by a player who was in the middle of looting mob corpses when his/her server crashed. According to an old database listing, the original use was (generally) "summon a brown horse or release it." (The actual text is in German. "Benutzen: Beschwört ein reitbares braunes Pferd oder gibt es wieder frei." I'm certain there is context that all the software translations I tried left out.)
In my opinion, this was likely a datamined item that wasn't nor intended to ever be available in the game. The item ID is very low and a lot of developer spells, items, etc. are found in very old data. I wouldn't be surprised if it was a leftover from vanilla beta.
Consumed on use. It grants one segment of rested experience, hence why it is ineffective above level 99. (Current maximum level is 100, and I imagine Blizzard doesn't want players hoarding the item for the next expansion pack.)