Well, I’m not the definitive source for the answer, but I might be able to help a little. Also, I’m currently in a hotel room, so I’ll be brief.
A 70% chocolate is usually called for in order to achieve a stronger chocolate flavor than a semisweet can deliver. Also, because a higher percentage chocolate contains more fat and less sugar than chocolate of a lower percentage, the texture is affected, so adjustments to the recipe have to be made accordingly. Usually, the type of chocolate is often chosen based on the cook’s/baker’s whim, so you could basically use any kind of chocolate you want, just so that you make the correct adjustments. In addition, certain chocolates work better with recipes better than others. As you probably know, each chocolate has its own flavor profile and characteristics, so where one chocolate might work wonderfully in a fruit-based dessert, another will work perfectly in a nut-based dessert. You also have to take into consideration the flavor and intensity of the chocolate itself, regardless of cocoa content, because, for example, a delicate chocolate such as Porcelana would essentially get lost in any dessert, whereas Guanaja would hold up very well with strong-flavored ingredients.