No, you don't have to salt your eggplant, because most eggplants today are bred to avoid bitterness. However, if your eggplant is large, it's more likely to be bitter, so you can salt it if you like. To do this, sprinkle the eggplant slices generously with salt -- at least 1 teaspoon of salt per eggplant -- and place into a colander over the sink to drain for an hour. (It seems like a lot of salt, but this is necessary for the eggplant to release enough moisture and its bitterness along with it.) Then, rinse with water and proceed with the roasted eggplant recipe as written.