This setting allows bot to automatically increase lot size as your balance grows. When you tick this box, a new textbox called DynamicLotSizeSettings appears. Specify the pairs and the balance per 0.01 lot size you wish to use. For example:

EURUSD-1000;GBPUSD-1000;XAUUSD-3000

The setting above means, it will play EURUSD at 0.01 per $1000, GBPUSD at 0.01 per $1000 and XAUUSD at 0.01 per $3000.

If you have $10,000 balance, it means bot will trade initial position at:

EURUSD 0.1
GBPUSD 0.1
XAUUSD 0.03