The difference between splittable and non-splittable activities is not what you think.
Splittable activities can be interrupted at any point and then resumed, but non-splittable activities can never be interrupted. Once they start, they have to be executed until they're finished without any interruption.
An example of a non-splittable activity is painting. You cannot just stop painting the building and then resume, as the color will differ.
Note that most activities are splittable.