Renown tactics use different slots than normal tactics. So basically, let's say I'm playing a Woodsman WL. Instead of having to drop Moraledrain to slot Loner to achieve the same damage that a mara does WITH moraledrain slotted- I can slot Loner in the renown tactic slot and be on par with Mara damage while slotting Moraledrain aswell.
That's all there is to it. At this point it's just there to let WL not waste a tactic slot on Loner for builds that have no use for the pet in the first place.