Indigo Terminal Emulator does have an adjustable backlog setting for defining how many lines of data should be kept in the terminal emulator's backlog. Indigo's backlog range is from 5 lines to 20,000 lines of backlog.
To access this setting, with a terminal session open, select the "Session" main menu and then the "Session Properties" menu item. The backlog setting will be located on the "Terminal" tab of the Session Properties dialog.
Applying a backlog at the high end of this range could affect application performance depending on the computer's CPU and memory resources available. Typically in general usage scenarios no performance degradation would be noticed.