Regular seed packs come out roughly half male, so several weeks of space and nutrients go to plants that get pulled at preflower. Feminized stock removes that step and produces female plants in close to every case, so the tent stays full. Strain listings with their reported female rates are laid out at https://queenfeminizedseeds.com if you want to compare breeders. The trade off is losing males entirely, which only matters if breeding is on your list.