Its pulling power. Ok, realistically one can take off about 12 wagons, but even then it is quite a lot for such a small model to pull.
https://youtu.be/QYVfbDc7NIw
Little Ruston.
Little Ruston.
Modelling On A Budget ---》 https://www.newrailwaymodellers.co.uk/F ... 22&t=52212