Opacity 0-1: Bad Idea?

In the world of computer graphics, there are generally two ways to do opacity.
They either range from 0 to 100 (aka 0$ to 100%).
or they range from 0 to 256 (thus mor in line with the 256 used to mix colors).

The first is perhaps easier to understand.
The second can be useful if you are doing something that needs to be exact.

However, I am fully convinced of W3's method of using a value from 0 to 1.  It seems neither easy (intuitive as in 0 to 100%) or exacting (as in the standard 256).
Also, if you can only use 0 .1 .2 .3 .4 .... to- 1   and not things like .13  for 13% then I believe this method is gonna be rather limiting in the future.

So I guess the question is can you only increment 10% at a time as in 0 (0%)  .1  (10%)  etc....?