Well, Variables are not that hard. I'm not saying that one should use them for everything, but if there is one task that does not exists as a block, why not? Variables are just some names that hold some values. The most complicated thing about them is their data type, but even this is not that hard. The one that is mostly used is "double" - this is for numbers.
I don't even recommend to use many Variables. I have seen some people using big list of Variables, but I think this makes everything much more complex, because you need to remember more things. But 1-2 Variables... this is almost nothing.
There are obviously some situations that the only way is to store some information in a Variable, like your situation. There is no way to know what was the Equity few hours in the past, because there is no history of Equity prices. Candles are some sort of history prices, but there is no such thing for Equity and Balance. Well, if you keep at least 1 trade opened, then Balance is actually a history value of Equity. Otherwise if you want to remember the value of Equity for later use, how can you do that? You use Variable. Again, there is no block that does something like "Give me Equity at 02:34", only because Equity is not something that MT automatically keeps into a history database.
Other things can be get from MT's database, things like candle prices (OHLC, Time and Volume), indicators data (which is modified version of OHLC), parameters of all orders and trades (SL, TP, Lots, OpenPrice, ClosePrice and others...). These values can be get from the past without using Variables, but sometimes the EA can be made faster if you store some of them in a Variable and thus make something like cache.
