What do the planets say?
They are considered to be more powerful than transits because they last so long. There are two kinds of progressions that Magi Astrologers use. The first is taking every day after birth to represent a year in the life of whatever is represented by the birthchart. In this way the chart for 30 days after the birth is the chart for the 30th year in the life of the person (or entity) in question.
The other type of progression is taking the progressed chart just mentioned and using that as a transit chart by laying it over the birthchart and seeing how they interact (i.e. what aspects exist between them).