Are expert advisors really helpful?

Depends. I used EA initially but then preferred taking things in my own control. There came a stage when I wasn’t aware what bids are being placed and when and what profit I’m making. However, I won’t deny that during the initial stages, they did prove helpful since I was unaware about where to place the stop-loss, and when to enter and exit the trade.

What’s the difference between robots and manual trading?

pure wisdom.

Of course, the advisors are really helpful, since the machine is not impulsive). Although, if the robot is in impulsive hands, it can also fail. Long-term calculation, cautious steady pace. Of course, it requires some investments. A good robot is expensive.
In addition, everything depends on the quality of internal maintenance of the robot, the trading system, and any indicators. Periodic optimization of settings will be just what you need. Of course, robot is profitable. A wider range of prices.
Everything is volatile, numbers change. So you have to understand that robots are robots and they act according to a certain program. But the market itself is not predictable and even with a robot, you cannot predict 100% of what is going to happen and make money on it. Were they able to predict the situation with the currency? And what about world events and the economy? That is impossible for a robot to predict.

EA seem good and no sleep, but how about if MT4 freeze and the EA stop working.
This can make your account in danger while you sleep.

For example, an EA for GBPNZD only, just reverse the order:
BUY LIMIT @ 1.948 and TAKE PROFIT @ 1.951 and
SELL LIMIT @ 1.951 and TAKE PROFIT @ 1.948

this up/down setting may readjust weekly or daily, don’t care high spread but stable pair.

I currently have 20 EAs running in a Metrader and have not had a single freeze in the last 2 years since they have been running.
If I have ever had an MT freeze, it was because EAs or indicators were badly programmed or during backtests when the hardware was not sufficiently dimensioned. Or both!

Even for humans, it is generally not 100% predictable. Unless you are a psychic at the fair. So why do people trade in the stock market anyway? Because there are rules (e.g. if this happens, then it is very likely that the price will rise). To help them, people take indicators that show them these rules. EAs do nothing else. Only without emotions. For that, EAs lack the overview of the whole. Only humans can do that at the moment.