Liothyronine is the drug of choice in treatment of:
Myxedema coma.
Cretinism
Iodine deficiency Goiter.
Non resectable causes of papillary thyroid carcinoma.
Myxoedema coma is an emergency condition; hence faster acting T3 (Liothyronine) is preferred over thyroxine (T4). For the other indications thyroxine is preferred because of longer duration of action.