Are built-in wrist rests bad for your wrists?

Probably yes. Most ergonomists say gel or foam wrist rests actually increase pressure on your carpal tunnel if you rest your wrist on them while typing. Your hands should hover, with your forearm supported by the desk or armrest. A wrist rest encourages planting your wrist, which compresses nerves and blood vessels over time. Unless you only use it as a palm support during pauses, skip it and get a flat, hard mousepad.