Sorry for the late reply.
If you set "RubberWorm crate rate" to 1, the only conspicuous change will be that the crate collection counter is enabled (shown at the lower left of the screen).
In your example, with 30% weapon, 0% utility, 20% health, 50% no crate, and "RubberWorm crate rate" set to 2, that means that at beginning of every turn, the crate drop logic is applied 2 times.
That logic is: First add up those percentages. 30+0+20+50 = 100. With a sum of exactly 100, that means they are actual percentages. So for example:
- there's a 50%*50% = 25% chance that no crate falls at all
- there's a 30%*30% = 9% chance that 2 weapon crates fall
- there's a 30%*50% + 50%*30% = 30% chance that 1 weapon crate falls
- there's a 30%*20% + 20%*30% = 12% chance that 1 weapon crate and 1 health crate fall
But when using the "no crate" setting, the percentages don't have to add up to 100. Whatever they
do add up to, is treated as meaning 100%.
So for example, 60% weapon, 0% utility, 40% health, 100% no crate would behave identically to 30% weapon, 0% utility, 20% health, 50% no crate.