the "i" stands for binary.
A kilo in decimal is 1000, it is 1024 in binary( 2.4 % difference)
A mega in decimal is 1000^2, it is 1024^2 in binary (7.3 % difference)
A giga in decimal is 1000^3, it is 1024^3 in binary (15.3 % difference)
as you can see, the difference is small in the beginning but it gets bigger and bigger and bigger and somebody can make a lot of money at your expense if they substitute one unit for another.
There is a proposal to use differentiate the decimal unit and and binary one. KDE is, by adding the "i", make it clear what unit it is using to avoid confusion