As soon as your jig breaks the waters surface and until it contacts the bottom, you're beginning the "fall." I catch about 70% of my fish during jig fishing during this fall.
The fall speed is an important part of getting good bites. In cold water, a slower fall does better. In hotter water, a faster fall tends to do better.
You can change your fall rate by using bigger bulkier tails to slow, or by downsizing the trailer to fall faster. I don't really fiddle with the trailer.
Instead, I use heavier or lighter weights of jig heads, keeping the trailer the way fish seem to find it most attractive at any given moment.
I find the skirt and trailer to be the most attractive part of the jig to a bass, so I choose them for fish appeal about color, shape, sound, vibration, action etc, and don't really worry about the weight of it.
I try different fall rates by varying the weight of the jig head, going to a heavier head for a faster fall and vice versa.
Line can also affect the fall. Thicker and/or inflexible line causes a slower, more arcing fall with more drag on the lure, whereas thinner and/or flexible line results in a faster, more straight down fall with less drag on the lure. This is not to imply that a thicker line is "bad" but that it does have an affect!