A sporangium is a spore-case or a receptacle for spores. Usually, this refers to sporangia (plural of sporangium) on a plant called sporangial. Most sporangial plants disperse their spores by using the wind. A few use water or animals.
Spores are better suited to broadcasting because they require less energy and material for the plant to produce. Spores are also very resistant to drying and mechanical damage. The disadvatage is that spores have less resources than a seed, and can only germinate in nearly perfect conditions.
The predictable microclimate is necessary to assure good conditions, but it need not occur often, as long as it occurs more often than a plant's lifetime.