We check everything that goes up on our Warehouse to make certain it works as advertised, so if you get it from there it does what it says it does. It looks like this was designed for heads up tournaments. If you're playing heads up it will tell you the size of your effective stack in big blinds (based on the last blind size) -- it gives you the smaller of your stack or twice the average stack minus your stack. That gets you your effective stack if you're heads up (as the average stack multiplied by two is the total chips in play), but at other table sizes it won't make much sense.
Again any stat in blue is custom so all black stats are always the defaults. This stat doesn't use any custom columns so you could just delete it if you wanted. Depending how many others you have it may be easiest to just delete the custom ones you don't want. You can set the drop down at the bottom left to show custom stats only so you don't need to scroll through the entire list, also.