Hot water is not a magic fix for every situation. You should seek other methods if:
Most toilet clogs are caused by organic material (waste, toilet paper) or oils and fats (if someone poured cooking grease down the drain, which should never be done).
Most toilets are made of vitreous china or porcelain. These materials are sensitive to "thermal shock." If you pour 212°F (100°C) water into a cold bowl, the ceramic can crack instantly, leading to a permanent leak and a very expensive replacement.