Although you can set the Budget so that you cannot exceed the budgeted amount (Prevent Exceeding), someone can still start a timer to do work and will not be alerted until after they stop the timer. It would be better to flag the account so that a team member cannot begin a timer at all if the budget has been exceeded.
How often would you use this request?
Monthly. We use this feature when we are waiting on retainer funds and do not want any work started until we receive a retainer.