Pressed powders are great for touching up or setting to makeup as a whole. However, you want to be careful if setting with pressed powders because the particles of powder are typically larger in order to be able to press them in compacts. Which means... And of course they are extremely handy to have on the go!
Loose powders are great for setting makeup because the particles of powder are typucally more finely milled and therefore can set the makeup without looking cakey.