EA are pre published mql applications that are designed to improve trading by forex trading professionals usually and they are designed to not waste time traders spend on market observe and dealing and improve profitability and What I know about EA is a forex robot can automatically perform trades automatically without us monitor. So I guess the use of the EA is to assist all traders with large capital, because EA typically uses shall have a minimum deposit of $ 1000, so far I've never tried it on a demo account though, because I have absolutely no interest in this.