MetaTrader 5 platform allows to backtest Expert Advisors so you can get the statistics for a decent period of time to calculate future perfomance according to previous results.
To ensure in trading strategy backtest is a vital requirment because it has to be tested on a decent time period to eliminate risks of occasional success.
Another vital feature of using Expert Advisors is eliminating emotions from your trading. Robots do not have senses so they act accordingly to the coded strategy.
Expert Advisors do not enlarge lots, make sensless entries, premature close positions and avoids other bad habits of manual traders.
For the traders that want to be involved in manual trading or when the trading strategy is intuitive, there exist indicators that could help them to make trading decisions.
Indicators are as well automated and their main difference from Expert Advisors is that they do not open, close or modify trades.
They can generate signals that can help trader to make a faster market analysis and spend time on other important aspects.