This is important to you as both a buyer or a seller. Let me give you an example to maybe help explain this.
Let's say you want to get solar panels on your home. Your choices are to purchase them outright, or to lease them from a company. If you want to move, what happens with the solar panels? If they're leased, what is the lease term? What if the lease isn't finished? If you purchased them, and they aren't paid for yet, do they have to be paid for with the proceeds of the sale? What if there isn't enough money to cover the remaining balance, or are you short selling the house?
If you're the buyer, and don't want the solar panels or the expense of the lease? Can they be removed? Would removing them damage the roof/surface and that may need to be replaced? Who is responsible for that?
The purpose of the addendum is to just make sure both parties are aware and agree to, as part of the contract, these leased types of items.