The dialog window “Data Horizon” serves to set limits on the historical data. These conditions are valid for the loaded data only. They do not concern the original files.
Maximum data bars - this is the maximum number of bars that will be loaded.
FSB needs 300 bars minimum to accomplish a correct calculation of the indicators. The maximum number of data bars is 50,000
1).
It becomes useful if you are conducting a “future test in the past”. For example, you do not allow loading of last month's data; you build your strategy and afterward cancel the limitation. If the direction of the balance line remains the same, it means that the strategy is (probably) not over optimized.