Having control on the amount that you deposit is even more important. Many online casinos impose maximum limits on deposits, but these are usually too generous. Their responsible gambling protocols allow you to set daily, weekly or monthly limits on how much you want to deposit. Once the limit is set then the casino will not accept deposits greater than it, because it would risk losing its operating licence. The limit can be increased, but the process is time consuming and cumbersome. You would have planned a gambling budget as indicated earlier and your set deposit limit should conform to that.
Some online gambling sites will allow you to set a limit on the amount you wager instead of the amount you deposit, but ultimately the objective and result is the same.