Comparing localizations across adjunctions

We show that several apparently unrelated formulas involving left or right Bousfield localizations in homotopy theory are induced by comparison maps associated with pairs of adjoint functors. Such comparison maps are used in the article to discuss the existence of functorial liftings of homotopical localizations and cellularizations to categories of algebras over monads acting on model categories, with emphasis on the cases of module spectra and algebras over simplicial operads. Some of our results hold for algebras up to homotopy as well; for example, if TT is the reduced monad associated with a simplicial operad and ff is any map of pointed simplicial sets, then ff-localization coincides with TfTf-localization on spaces underlying homotopy TT-algebras, and similarly for cellularizations.