A lot depends on your intended use and where you'll be, and when, but assuming you're talking a new unit option (not some aftermarket add-on) then if you are anywhere but the deep south anytime between mid-Sept. and mid-May, I'd suggest it (maybe even then). You may not expect to need it, but I hear that even central Florida gets some occasional freezing weather. If it were me, that would be a must.
Just FYI, when you're asking about RV stuff it's often helpful to know what kind of unit is involved: make, model, motorhome, pop-up, fifth wheel, travel trailer, truck camper? There are so many variations that general answers sometimes don't apply. Putting your unit in your signature can aid you and us.