It's always an option when flying on a 2.4 system, although ignition manufacturers recommend against it. For the insignificant amount of weight incurred from using a separate battery and switch that's offset by the enormous amount of additional rf safety I wouldn't do it. If you're flying a plane so small it can't handle the weight of an ignition battery it might be better off glow or electric powered.

If you're flying a 72mHz system you might be considered a couple bricks out of balance to run a single battery receiver/ignition system. I sometimes think manufacturers of certain products are trying to artificially move up that airplane expiration date. They are the only ones that end up with actual benefits from some of the products out there.