You don't really need one. But it depends on your lifestyle and your anxiety level. If you're going somewhere with limited public charging availability and you will cut it close to get back to a charge station, you may want to take your cable with you or carry an extra cable (there are several on the market that are suitable. Tesla portable cables are plentiful on eBay, you just need a J1772 adapter. In this situation, you may only have access to an 110 outlet, so you would need to be staying there for a while, like a day or so to get enough milage at the rate of 1-2 MPH charging to get you enough miles in the car to get you back to a faster charger, its a matter of planning ahead.