The size of a turbine goes hand in hand with it's efficiency in general. Smaller turbines generally use more fuel to provide a given amount of power, because the tolerances become so important cost of production is increased. Another factor is rpm, the smaller it is the faster it has to turn. On the extreme side of things model turbines can spin over 140,000rpm
. That kind of Rpm requires bearing replacement frequently (don't remember the specific time frame).