Saving money. Group travel is generally much cheaper. You can get group rates on accommodations (you've probably seen brochures that say single occupancy, double occupancy, triple occupancy, and so on - the price goes down for each person sharing a room), companion rates for certain modes of transportation (particularly bus and train), group rates into attractions (amusement parks, museums, etc), and there are tons of other things you can split costs on. If you're able to reduce costs, you'll have extra money to see and do more things.