In the middle of TNG : Lessons, the crew of the Enterprise-D is flying on a rescue mission toward Bersallis III, to save a Federation outpost from an impending fire-storm.
Upon reaching Bersallis III’s system, the ship drops out of warp. During senior officers meeting Riker states that it will take another hour to reach Bersallis III, so LaForge's team will have another two hours for a rescue transportation. When Riker tells this, we can clearly see, through windows behind him, that the ship is indeed travelling on conventional engines.
Why? Wouldn't it be more efficient in terms of rescue mission, to fly in warp until reaching the planet and not to waste another hour of precious time travelling?