I believe that Franklin was probably referring to money at the time, but this statement also applies to automobiles. Loaning your car, or borrowing one, is a bad idea. The potential consequences to the insurance of the car’s owner can be most unfortunate.
The liability coverage for a car follows the car. If I borrow your car, it is your insurance that would pay others in the event I injured them or damaged their property. You are legally responsible for what I do with your car. Do you have enough protection should your son or daughter loan your car to their college roommate? Do you want your premiums affected by something that someone else did while they were borrowing your car? It can get very awkward VERY quickly.
Car insurance contains all sorts of coverages. Liability follows the car, but the medical and uninsured/underinsured motorist coverages follow the driver. When it comes to cars and liability insurance, keep things simple. As Franklin said “Neither a borrower nor a lender be.”