I use primers as well. Initially, I didn't want to use it because I thought it would clog my pores, but the reverse is actually the truth. Instead of clogging pores, primers help prevent pores from being clogged. It acts like a silicone to fill up open pores and make skin smoother all over.
I also love how primers can make my makeup last longer as it reduces the secretion of oil. I use Smashbox and a cheaper one from The Face Shop (a Korean chain), both of which work well.
I heard that some apply primers after putting on makeup. Has anyone tried this?