An example:
A student is taught how to calculate an integral with MathCAD on a school PC. They now know how to use MathCAD on Windows to calculate an integral. If the OS or software changes, they may lose that knowledge, and they may not understand the concept. They've effectively 'lost' knowledge due to time moving on.
Differently:
A student is taught how to calculate an integral with pencil and paper. Due to pencil and paper doing nothing without the student driving it, they must understand the steps to the process, and in doing so, will likely get to understanding why those are the steps. At the very least they may be curious about the steps, why they work, and why all are required. If you give them a PC, they'll likely be able to figure out how to use it, as they understand the concept. If you take away the PC, they'll still be able to use pencil and paper.
The distraction/multitasking angle is interesting too, but I really think education works best when you take all unnecessary power away from the student. They are forced to learn the concepts rather than get lost in all the peripheral details (PC, software, notifications, etc.) and understanding of fundamental concepts will rarely become useless. While understanding of computing platforms or software versions will very quickly become useless.