Because it decreases the escape angle of the light to avoid spillage but in doing so it also makes the light less soft and more contrasty which is the opposite of what a softbox should be. The only time you need to use a grid on a softbox is if you're working in a very small space and you need to stop light spilling onto your background or other areas, but you can also do this with simple flags instead.
I saw some of your videos and honestly you are 1 of the best I have ever seen and learnt much from your free videos and willing to apply in your school or academy soon, But I still don't understand why when I shoot with soft box my photos appear to be a little bit flat I used to shoot with scrim and diffuser but you encouraged me to buy a soft box because most of your videos you use soft box I work as recipe development and photographer but using soft box specially in light airy photos maes me feel so flat, when I see your work the results is completely different
