Any load fed via a tuner can be useful. But there are problems where a proper non-reactive wideband non-radiating load is required to fix them - and strings of lightbulbs etc will radiate.
Light bulbs don't radiate more then unshielded resistors.
What is the purpose of a wide band resistive load, when your real load will be an antenna transformed by a tuner to 50 ohm?
So a water cooker transformed to 50 ohm by a tuner is a more realistic testload then a pure resistance load of 50 ohm over a wide band.