Modified sine wave inverters can be used for simple systems that don’t have any delicate electronics or audio equipment that may pick up the choppy wave and produce a hum. Motors with brushes and old tube TV’s are usually ok with the modified sine wave. Some equipment may seem to be working fine, but it may run hotter than with a pure sine wave and reduce the life of it.
Pure sine wave inverters can be used on all electronic equipment and will not have any side effect. A pure sine wave inverter is more expensive than a modified sine wave inverter.