Why is it not recommended to leave cryptos on exchanges? Can you explain? I'm a beginner

Dear friends, there are thousands of variants and possibilities, depending on your profile (conservative or aggressive), your expectations regarding 3x, 10x or 30x gains.
It depends on your willingness to study and whether you like to follow the market or just want to make a few $$ without going into too much depth, etc...
Therefore, it is difficult to recommend a crypto, but BTC should always be in your portfolio, buy whenever you can. (there is an “automatic investment” option on BINANCE where you can invest $0.1 per week per day or per hour.