I do that to increase the profits. RoboMiner Pro opens and closes trades every 40 pips. By adding a second instance with the 'Shift' = 20, and a new magic number, RoboMiner Pro will open trades that are offset from the first instance by 20 pips. That means instead of trades only every 40 pips, I will now have trades every 20 pips. This increases the risk, of course, but it also increases the likelihood that one of my trades will close as now I don't have to wait for the market to move a full 40 pips.
I have just today changed my settings to have 4 instances now, each with a 10 pip shift from the next (so Shift = 0, 10, 20, and 30 and a unique magic number for each instance) in hopes of picking up more profits. I have also decreased my lot sizes to 0.01 which is still quite high risk for my account balance. 0.01 lots are the recommended size for a $2000 balance, so you can see I am over 4x as high risk as recommended.
I'm a lazy trader. I like to make money while I sleep.