In this video, photographer Francisco Hernandez goes over a few lighting modifier options, ranging from very large to fairly small and shares the differences between each light and in what situations each may be better to use.
Specifically, the three light modifiers that Hernandez mentions are a 5-foot Octabox, a 36-inch Octabox, and an 18-inch Octabox. Starting with the smallest of the three, he goes over the characteristics of the light, its positive aspects, and its negative aspects. He does this all while shooting with a model and showing examples so that you can see exactly what he is talking about.
After the 18-inch Octabox, Hernandez moves up to the 36-inch model, and here the produced light is softer and looks better overall on the subject. However, the bigger the light gets, the more unruly it gets outdoors, where it is more likely to catch the wind and be blown down, and of course it’s also a bit more of a pain to pack up and travel with.
It is more of the same from the 5-foot model, with the light looking even better, but the light itself being even more of a chore to pack around and use outdoors.
In the end, the big takeaway you should have from this is that when it comes to lighting, size does matter and bigger is almost always better.