Purpose of any budget is A 3C DE PM (i.e. Authorization, Controlling, Coordination, Communication, Delegation, Evaluation, Planning and Monitoring)
Flexible budget recognises changing nature of costs with changes in output level.
It helps in comparison and/or forecast.
For this corresponding flexible budget is revised to give a flexed budget at desired production level.
Flexible budget revised at actual activity level is called flexed budget.
Flexed budget identifies the (variable, semi-variable, step fixed and fixed) nature of costs with the change in volume.
Source: Fixed, Flexible and Flexed Budget