Seclusion can often be implemented when the unit is under-staffed. If that situation is common then so will be seclusion, for all the reasons Diasi suggests. Such a patient needs 'special' staffing which is expensive. On the other hand the tariff for her care will also be expensive, sometimes £2-3000 per week. A modern mental-health care unit can't handle such cases easily and historically, never have been able to without restraint, heavy medicating or seclusion. Often in combination.