The width of bands directly affects the draw power.
If, for example, 2 bands of 2 cm each wide Thera-band Gold stretched 5 times, say, from 15 cm active length to 75 cm total draw length has some 5 kg of strength, then 2 bands 1 cm each in width should have half of that power - or so.
When I learned how to cut the bands I first listened to the advice to first find what maximum power I can stretch - which I found out by cutting couple of various widths of bands, measuring their strength at 5x stretch ratio. let us say that I found out that 2 bands 3 cm wide each is my maximum where my hands shake seriously . But then I took off some 30-40 % of that power I came to 18-21 millimeters of my elegantly manageable width (read power).
Of course, I tried all the widths from 12, 15 mm, 19 mm, 20, mm etc. and I have a very good feeling now of each of them.
In my experience, when you do target shooting you do not need much power and smaller ammo will do.
For plinking I cut TBG 18 mm wide, sometimes only 15 mm and the marbles still fly very well.
When hunting there are some, I believe, lower limits of power/velocity/energy for various game, but the hunters can tell you that.
In essence, and I think that everybody will agree that optimum draw power is related to an individual and to a purpose in various degrees.