Do not leave on passive! I did and had mine outside my base so I could quickly go out and do a swing of the tail and get a ton of berries. A while later I get message saying that a lv4 pego had worked down its 2500 health and killed it.
Bronto's are a beast! Make a platform saddle, have mortar and pestles on it, carry spoiled meat and you will make thousands of narcotics in no time! Also a great thatch gatherer, would definitely recommend taming the Bronto.
Build a platform with furnaces and storage on it's back, take it out to a metal filled area, gather metal all whilst dumping it into it's inventory. When your done put all the metal into the massive amount of furnaces you have on it and smelt it up, then store it!