Not a weaning mode, as at any rate they are getting complete mechanical support. Some authors feel this is a more friendly mode for awake patients. As a final mode prior to extubation in some patients. Every patient is different and it is hard to know exactly what a patient will need in terms of ventilatory support until they are actually on the ventilator. So many of us a have preset ideas as to where to start any patient and then adjust the ventilator afterwards to achieve the desired ventilation effect.
Pressure support is only helpful if the patient is going to be spontaneously breathing.
A good place to start. You can always adjust later. For small children this is lower that their usual spontaneous rate but with the larger tidal volumes that are delivered this increases the minute ventilation. Not so high as to cause problems. Allows maximal preoxygenation in case anything happens.