Preview items you see in game, either in inventory, exchange or shop. You always see what you are supposed to see. You certainly won’t notice a drop in performance by hovering over the next item.
Preview of armors
You are able to see how an armor looks like. Shows the relevant character for the selected item.
Preview of weapons
You are able to see how a weapon looks like. Shows the relevant character for the selected item.
Preview of costumes
You are able to see how a costume looks like. Shows the relevant character and gender for the selected item.
Preview of anything else
If you have something else to show, no problem, I will implement preview of it. Mounts, pets, sash, emblems, no problem, you get it.