It is very standard when you buy a home to take over certain rental contracts. The most common is the hot water heater; in southern Ontario at least, it is far more common to rent a hot water heater than to own one, and generally the contract is transferred to the buyer on closing as agreed to in the purchase contract. You could also assume a furnace rental, or an alarm system contract.
You don’t have to assume anything, though. You might want to review the contracts before you agree to any of them, to see if you are happy with the terms. As a seller, you will want to know well in advance if the buyer is not taking on any rental items, because that means that you will have to buy out or cancel a contract.