12V will work for many car uses, but can be a little low for some of the bigger dual chargers on 1/8 scale and monster trucking packs though. Remember most of the bigger chargers have input current limits, in many cases the full power and amp output of a 12V server supply is not usable. In my own case what some would consider a moderate power charger needs at least 15V to reach it's 360W capability.

24V supplies can be very useful for the larger plane and heli guys. 12S and bigger packs are not unheard of. 24V can even be limiting at the extreme.