Tim, for lack of a better word, sucks. He puked when the jeep is falling down the tree, he did pretty much nothing to stop aiming the flashlight in the T-Rex's eye, he was so slow getting over the fence that he got electrocuted, and he told the LAMEST dinosaur jokes possible.
But mainly, it all comes down to the scene where Lex is trying to hack the security system while Dr. Grant and Ellie are trying to shut the doors on the raptors. During this scene, what's Tim doing? Oh, right - ABSOLUTELY NOTHING.
If only, Jurassic Park. If only.