1. Sometimes, rooms look better when furnished to give the potential buyer/renter an idea of how to lay our furniture and what the rooms could look like. It's all part of staging
2. Unless the owner/landlord specifies it in the contract, most places are sold/leased empty.
3. You don't buy/rent the place furnished unless it's in the contract that the place will be rented furnished, or sold with furniture. It's all part of presentation.