The real estate around SMT lines is very expensive, and the optimum way to load components at the side of the SMT line is on feeders which take reels. The reason is that a reel width could be 24mm, whereas the tray length could be 150mm. So if you try to load your components directly from the tray, they won’t load as quickly as from reels, but they take up much more feeder spaces. The whole idea is to be able to compact your feeders so that when you present the components in reels, they take up much less space.