do i need ballast resistor?

I use a 30 in mine and have never blown it with all the running lights, headlights, wipers, stereo and four brake lights and heater blower.
Of course I carry a 60 just in case but it's been almost 2 years since I put the 30 in it.
Some say you should use something capable to carry the max alternator output, but the cars pretty much never use that kind of load.