A left-exact localization of a category is a reflective subcategory such that the reflector preserves finite limits. There are several prominent examples of such localizations, such as sheafification, and localization of module categories. Is there a general theory of such localizations?

I don't have any particular type of result in mind, but given the prominence of the two examples I mentioned, it seems like the topic of left-exact localizations must have been studied for its own sake.

Locally presentable and accessible categories] and, of course, the theory of left exact localisations of presheaf toposes is just the theory of Grothendieck topologies. – Zhen Lin Apr 23 '13 at 7:47